ELECTRICAL 

MINING 
INSTALLATIONS 


P.W  FREUDEMACHER  A.M.I.E.E. 


ELECTRICAL  INSTALLATION  MANUALS 


From  D.  VAN  NOSTRAND'S  LIST 


The   " 


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INTRODUCTION     TO     THE     CHEMISTRY     AND 

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ELECTRICAL    MINING 
INSTALLATIONS 


/ 


INSTALLATION   MANUALS. 


CONDUCTORS,  HOUSE  WIRING,  ETC. 

LAMPS,  SWITCHES,   FITTINGS,  TRANS- 
FORMERS. 

ARC  LAMPS. 

MOTORS  AND  SMALL  POWER    PLANT. 

SHIP  WIRING  AND  FITTING. 

MINING  INSTALLATIONS. 

MILL  AND  FACTORY  WIRING. 

BELLS,  TELEPHONES,  ETC. 

TESTING  AND  LOCALIZING  FAULTS. 


ELECTRICAL 

MINING 
INSTALLATIONS 


By 

P.  W.  FREUDEMACHER 
A.M.I.E.E. 


NEW  YORK 
D.    VAN    NOSTRAND    COMPANY 

23  MURRAY  and  27  WARREN  STREETS 
1911 


'="7 


BUTLER  &  TANNER 

THE  SELWOOD  PRINTING  WORKS 

FROME  AND  LONDON 


PREFACE 

THIS  volume  has  been  written  especially  for  colliery 
engineers  and  contractors  engaged  in  the  installation 
of  electrical  plant  for  mining  purposes. 

The  first  chapter  deals  briefly  with  the  elementary 
principles  of  electrical  engineering,  special  reference 
being  made  to  alternate  current  working.  Many 
readers  will  already  have  a  sufficient  knowledge  of 
these  principles  and  for  them  the  volume  will  be  a 
guide  to  the  application  of  electric  power  for  mining 
work. 

Readers  who  are  engineers  but  not  essentially 
electrical  engineers  will  find  this  opening  chapter  of 
service,  and  it  is  hoped  that  the  notes  on  alternate 
current  working  will  clear  up  the  many  abstruse 
points  on  this  subject  and  give  a  working  knowledge 
of  the  terms  and  quantities  involved. 

The  author  has  described  various  classes  of  plant 
for  all  mining  purposes  and  has  given  formula  and 
tables  so  that  the  necessary  calculations  in  regard  to 
power,  outputs,  etc.  may  be  made.  It  is  impossible 
to  avoid  mathematics  altogether  in  a  practical  book 
for  engineers ;  but  examples  have  been  carefully 
prepared  in  order  to  show  how  the  more  elaborate 
calculations  are  to  be  accomplished. 

The  last  chapter  on  electric  winding  systems  has 
v 

43H577 


vi  PREFACE 

been  included  to  complete  the  subject  opened  up  in 
the  previous  chapter,  and  although  the  installation 
of  a  main  winding  engine  is  perhaps  a  matter  for 
experts  in  this  particular  branch,  the  volume  would 
not  have  been  complete  without  reference  to  this 
matter. 

P.  W.  F. 


CONTENTS 

CHAPTER    I  PACT; 

GENERAL  PRINCIPLES        ......         1 

CHAPTER    II 
GENERATING  PLANT          .         .        v        .         •        *       11 

CHAPTER    III 

GENERATING  STATION  SWITCHGEAR    .      •    •         •         •       23 

CHAPTER    IV 
TRANSMISSION  .  ' ^       39 

CHAPTER   V 
UNDERGROUND  CABLES  AND  FITTINGS        ...       62 

CHAPTER    VI 
ELECTRIC  HAULAGE 87 

CHAPTER    VII 
ELECTRIC  PUMPING  .         .         .         .         .         .         .107 

CHAPTER    VIII 
ELECTRIC  COAL  CUTTING  AND  DRILLING    .          .         .123 

CHAPTER    IX 
ELECTRIC  VENTILATING    .         .         *  .         .     129 

CHAPTER    X 
ELECTRIC  WINDING  .         %         .         .  .     134 

CHAPTER    XI 

ELECTRIC  WINDING  SYSTEMS 146 

vii 


viii  CONTENTS 

CHAPTER    XII 

PAGE 

SPECIAL  RULES  FOB  THE  INSTALLATION  AND  USE  OF 

ELECTRICITY     .         .         .         ,        V        .    -  .  163 

Definitions  .          .          *          *         .         ...  163 

Section  I.  General          .         .         *         .         .  .  164 

„     II.  Generating  Stations  and  Machine  Rooms  .  168 

„   III.  Cables     .        .....          •          •          •  .  169 

„    IV.  Switches,  Fuses  and  Cut-outs          .  .172 

'„      V.  Motors      '      .   '      . '  »      .          .         V  .  172 

„    VI.  Electric  Locomotives      .          .          .  .  174 

„  VII.  Electric  Lighting   .          ....          .       ,  >  175 

„  VIII.  Shot-Firing   .          .          .          .          .  .  176 

„    IX.  Signalling       .          .          ,          .          .  .177 

„      X.  Electric  Relighting  of  Safety  Lamps  .  177 

„    XI.  Exemptions  and  Miscellaneous            .  .  178 

INDEX      .         .          .         »         .         .                   .  .  179 


LIST  OF  ILLUSTRATIONS 

FlG.  PAGE 

1.  Alternating  Pressure  and  Current  Curves  .         .5 

2.  Curves  showing  Three-Phase  and  Two-Phase  Sys- 

tems .          .          .         .         .     '    .         .         /        6 

3.  Curve  showing  Pressure  and  Lagging  Current  with 

Resultant  Power  Curve        .          ;          ."         .         9 

4.  Diagram   of   Connexions  for   Compound   Wound 

Interpole  Generator     .          .          .         *         *       16 

5.  Connexions  for  Three-Phase  Windings  .          .         »        17 

6.  Diagram  of  Connexions  for  Continuous  Current 

Switchboards       .         .         ...         •         .       26 

7.  Diagram  of  Connexions  for  Three-Phase  Switch- 

board         .          .          .         J         .         .         .:      ^8 

8.  Section  through  Three-Phase  Switchboard     .          .  .     31 

9.  Continuous-Current  Leakage  Indicator  .          .       35 

10.  Diagram  for  Three-Phase  Leakage  Indicators  .       37 

11.  Poles  for  Transmission  Lines     .                   .  .46 

12.  Terminal  Pole .48 

13.  Shaft  Cable  Suspenders  - 67 

14.  Method  of  Running  Cables  in  Roads          .  .       69 

15.  Flexible  Cable- Suspender  .          .         .         .  .       71 

16.  Shaft  Cable  Junction  Box          .          .          .  .       72 

17.  Road  Cable  Junction  Boxes      .         .         .  .       73 


x  LIST  OF  ILLUSTRATIONS 

FlO.  PAGE 

18.  Road  Cable  Junction  Boxes      ....  74 

19.  Calender's  Gate-end  Box  .          .         .          .78 

20.  Fisher's  Patent  Gate-end  Box  and  Plug     .          .  80 

21.  Plug :    Fisher  Patent  System     .          .         .          .  82 

22.  Plan  of  Main  Haulage  Gear      .         .         ,         .  87 

23.  Main  and  Tail  Haulage' Gear    .         ...  89 

24.  Reversing    Controller    for    Continuous     Current 

Motors        . 93 

25.  Three-Phase  Reversing  Controller       ...  94 

26.  Section  through  Turbine  Pump           .     '    .          .  109 

27.  Characteristic  Curve  of  Turbine  Pump        .          .  112 

28.  Auto  Transformer  Starter  Diagram       .     ,      .         *.  113 

29.  Star  Mesh  Starter     .     .    .         ...         .  114 

30.  Winding  Engine  Load  Curve     .        ^         .          .  135 

31.  Types  of  Winding  Drums           .          .          .         '.  143 

32.  Siemens-Ilgner  Winding  System          .         *         ,  149 

33.  Winding  Engine  Load  Curve     .      ,    .         .         .  151 

34.  Crompton  Winding  System        .         .         ...  153 

35.  Westinghouse  Winding  System  .          .    .     .          .157 

36.  Westinghouse  Winding  Engine  and  Control  Gear    .  160 


LIST  OF  TABLES 

NO.  PAGE 

—  Particulars  of  Conductors  .          ...          .  52 

—  Particulars  of  Conductors  .          .          .          .          .  54 

I.     H.P.  Required  for  Main  and  Tail  Haulage  at  10 

Miles  per  Hour  .         .         .         .         .         .  98 

II.     H.P.  Required  for  Endless  Rope  Haulage  on  Road 

1,000  Yards  Long        •   ,      •          •          •          •  " 

—  Approximate  Friction  in  Feet  Head  per  Yard  of  Pipe  118 


CHAPTER    I 
GENERAL  PRINCIPLES 

THE  use  of  electric  power  for  mining  work  repre- 
sents one  of  the  greatest  developments  in  the  elec- 
trical industry  during  recent  years.  It  is  of  course 
understood  that  electricity  is  utilized  only  as  a  means 
of  transmitting  power,  which  has  to  be  generated 
in  the  first  place,  e.g.  by  burning  coal  and  raising 
steam,  which  is  turned  into  mechanical  power  by 
the  steam  engine,  then  converted  into  electrical 
power  by  means  of  the  dynamo  or  electric  generator, 
and  back  again  into  mechanical  power  for  use  at  the 
various  places  where  it  is  wanted. 

The  power  might,  of  course,  be  transmitted  by 
means  of  compressed  air,  by  hydraulic  means,  or 
in  certain  cases,  by  running  steam  pipes  from  a 
boiler  to  the  spot  where  power  is  required  and  there 
installing  a  steam  engine.  Compared  with  the 
transmission  of  energy  by  this  means,  it  must  be 
admitted  that  electricity  is  more  convenient  and 
efficient. 

At  first  sight  it  would  not,  perhaps,  appear  to 
have  any  great  advantage  from  an  economic  stand- 
point, but  the  gradual  development  of  the  industry 
has  shown  that  electrical  equipments  must  play  a 
very  important  part  in  all  up-to-date  colliery  instal- 
lations. 

With  electric  driving  the  generating  plant  can 
be  installed  in  one  central  station  (instead  of  being 
scattered  as  was  generally  the  case  before  the  advent 


2     ELECTRICAL  MINING  INSTALLATIONS 


of  electee:  Driving)  $&&  from  the  main  switchboard 
power  circuits  can  be  run  to  places  where  energy  is 
required  for  winding,  hauling,  pumping,  ventilating, 
coal-cutting,  lighting  and  other  work. 

Electricity  lends  itself  admirably  to  ease  in  dis- 
tribution, over  wide  and  scattered  areas,  with  the 
utmost  economy,  and  at  the  same  time,  additions 
and  extensions  can  be  readily  carried  out.  Taking 
everything  into  consideration  it  is  obvious  that  this 
method  of  power  transmission  has  great  advantages 
for  colliery  purposes. 

In  a  few  cases  power  may  be  provided  by  a  supply 
authority,  in  bulk,  but,  more  generally,  each  colliery 
will  have  its  own  central  power  station  to  generate 
the  electrical  energy  required.  In  most  cases  this 
latter  course  is  justified,  for  fuel  is  cheap,  and  power 
can  thus  be  generated  at  a  low  cost. 

Before  dealing  with  the  matter  of  generating  plant 
we  will  consider  for  a  moment  the  question  of  choice 
of  systems.  Electrical  energy  for  lighting  and  power 
purposes  may  be  supplied  as  continuous  or  as  alter- 
nating current,  the  latter  being  sub-divided  into 
single-  two-  and  three-phase  current.  The  choice 
of  the  system  to  be  adopted  depends  upon  many 
circumstances,  and  can  only  be  settled  after  full 
consideration. 

The  continuous  current  system  may  be  very  suit- 
able for  small  installations,  where  the  distances  are 
not  great,  nor  the  conditions  severe,  and,  in  all 
probability,  for  a  small  installation,  continuous 
current  will  prove  cheapest  in  the  long  run. 

For  large  installations,  however,  alternating-cur- 
rent working  is  almost  a  necessity,  and  in  many 
cases,  where  the  power  station  is  situated  at  some 
distance  from  the  shaft,  or  the  workings  extend  to 
a  considerable  distance  underground,  it  is  necessary 
to  work  on  the  high-tension  alternating-current 
system.  It  is  customary  to  adopt  a  three-phase, 
high-tension  system  in  such  cases  ;  two-phase  is  very 


GENERAL  PRINCIPLES  3 

seldom  used,  and  single-phase  is  never  considered 
for  power  work  of  this  nature. 

It  will  be  as  well  to  set  out  clearly  the  principles 
of  the  various  systems  and  their  relative  advantages. 

Taking  the  continuous  current  system  first,  it  is 
presumed  that  Ohm's  law  is  familiar  to  all — 

E=c,  or  ?=B,  orE^C.R. 
Jt\»  O 

When  E  =  Electro-Motive  force  or  E.M.F.  in  volts. 
„       R  =  Resistance  in  ohms. 
, ,       C  =  Current  in  amperes. 

From  the  third  expression,  E  =  CR,  we  can 
obtain  the  pressure  lost  in  any  conductor  due  to 
resistance. 

If,  for  example,  we  know  that  110  yds.  of  19/16 
cable  has  a  resistance  of  -044  ohm,  then,  with  a 
current  of  60  amperes  flowing,  there  will  be  a  loss  of 
60  X  -044  =  2-64  volts. 

It  is,  of  course,  understood  that  the  resistance  of 
the  total  length  of  cable  must  be  taken,  i.e.  lead  and 
return. 

Power  in  a  continuous  current  system  is  repre- 
sented by  the  product  of  volts  and  amperes,  E  X  C  = 
Watts  ;  but  in  dealing  with  large  values  it  is  more 
usual  to  talk  of  Kilowatts  (K.W.),that  is  1,000  watts. 
Since  E  X  C  =  Watts  or  W.  it  follows  that  the 
energy  lost  in  transmitting  electricity  through  a 
conductor  is  given  by  the  expression  :  Lost  Volts  X 
Amps., but  since  Lost  Volts  =  Resistance  X  Amps., 
the  energy  lost  may  be  represented  by  the  formula 
C  X  C  X  R  or  C2R. 

Prom  these  calculations  it  will  be  seen  that,  in 
order  to  limit  the  lost  volts,  or  "  pressure  drop " 
as  it  is  more  often  called,  and  also  to  limit  the  energy 
or  watt  loss,  it  is  necessary  to  provide  a  conductor 
of  ample  size,  especially  when  electricity  has  to 
be  transmitted  over  great  distances.  The  alterna- 
tive is  to  increase  the  voltage,  and,  by  so  doing, 
not  only  is  the  pressure  drop  reduced  in  proportion 


4     ELECTRICAL  MINING  INSTALLATIONS 

(because  for  a  given  power  the  amperes  are  reduced 
proportionately)  but  this  pressure  drop  bears  a  still 
smaller  ratio  to  the  increased  voltage. 

As  a  matter  of  fact,  the  percentage  pressure  drop 
is  improved  in  proportion  to  the  square  of  the  vol- 
tage, so  that,  by  doubling  the  voltage,  our  percentage 
pressure  drop  becomes  only  one-fourth,  assuming 
the  same  amount  of  power  to  be  transmitted  through 
a  given  conductor. 

Now  on  glancing  for  a  moment  at  our  formula 
for  energy  loss — C2R — it  will  be  noted  that,  under  the 
same  conditions,  our  lost  watts  will  only  be  one-fourth 
with  twice  the  pressure.  It  will  thus  be  seen  that 
it  is  advisable  to  adopt  as  high  a  pressure  as  prac- 
ticable, consistent  with  safety  and  ease  of  working. 

Before  going  further  it  will  be  advisable  to  define 
the  limits  of  pressure  as  fixed  by  the  Home  Office  in 
connexion  with  the  use  of  electricity  in  mines  : 

(A)  Low-pressure    supply — where    the    conditions 
of  supply  are  such  that  the  pressure  at  the  terminals 
where  the  electricity  is  used,  cannot  exceed  250  volts. 

(B)  Medium   pressure — where    the    conditions    of 
supply  are  such  that  the  pressure  at  the  terminals 
where  the  electricity  is  used,  between  any  two  con- 
ductors, or  between  one  conductor  and  earth,  may 
at  any  time  exceed  250,  but  cannot  exceed  650  volts. 

(C)  High-pressure  supply — where  the  conditions  of 
supply  are  such  that  the  pressure  at  the  terminals 
where    the    electricity   is    used,    between    any    two 
conductors,   or  between  one  conductor  and  earth, 
may  at   any  time  exceed   650   but  cannot  exceed 
3,000  volts. 

(D)  Extra  high-pressure  supply — where  the  con- 
ditions of  supply  are  such  that  the  pressure  at  the 
terminals  where  the  electricity  is  used,  between  any 
two    conductors,    or    between    one    conductor    and 
earth,  may  at  any  time  exceed  3,000  volts. 

We  will  now  take  the  case  of  an  alternating  current 
system,  and,  as  three-phase  is  used  almost  exclusively, 


GENERAL  PRINCIPLES  5 

we  will  confine  ourselves  practically  to  a  consideration 
of  this  system,  although  the  remarks  may  be  taken 
as  generally  applicable  to  single-phase  and  two- 
phase  systems  of  supply. 

As  is  well-known,  single-phase  alternating  pressure, 
or  current,  may  be  represented  by  a  sine  curve 
(Pig.  1,  A)  from  which  it  will  be  noticed  that  the 


FIG.   1.     ALTERNATING  PRESSURE    AND    CURRENT    CURVES. 

current,  or  pressure,  starting  from  zero,  increases 
to  a  maximum,  decreases  to  zero  again,  then  reverses, 
increases  to  a  maximum  in  the  other  direction,  and 
again  decreases  to  zero,  this  being  termed  a  cycle 
or  period,  usually  referred  to  as  the  frequency  or 
periodicity,  and  expressed  in  so  many  cycles  per 
second. 

The  frequency  is  usually  of  the  order  of  25-60 
cycles  per  second,  although,  in  special  cases,  it  may 
be  as  low  as  15  for  railway  work,  or  as  high  as  100 
for  lighting  purposes  in  scattered  districts. 

These  special  cases,  however,  do  not  concern  us 
at  present,  and  it  may  be  taken  that  50  cycles  has 
practically  been  adopted  as  standard  for  lighting 
and  power  work,  and  25  cycles  as  standard  for 
extensive  power  supply  only. 

The  illustration,  Pig.  1,  B,  shows  the  pressure  or 
voltage  curve  for  a  single-phase  supply  in  full,  and 
the  current  curve  in  dotted  lines  ;  further,  the  two 
curves  are  shown  "  in  phase,"  that  is  to  say  the  vol- 
tage and  current  curves  both  pass  through  the 
zero  point,  and  both  reach  their  maximum  at  the 


6     ELECTRICAL  MINING  INSTALLATIONS 

same  time  ;    but  it  by  no  means  follows  that  this  is 
so  in  all  cases,  as  we  shall  see. 

The  three-phase  system  may  be  described  as  three 
single-phase  systems,  so  arranged  as  to  differ  in 
phase  as  shown  in  Pig.  2  (A),  while  the  two-phase 
system  is  equivalent  to  two  single-phase  systems  ar- 
ranged to  differ  in  phase  as  shown  in  Fig.  2  (B). 


FIG.  2.     CURVES  SHOWING  THREE-PHASE  AND  TWO-PHASE 
SYSTEMS. 

:  We  will  not  enter  into  further  detail  here,  in 
regard  to  these  alternating  current  systems,  which 
are  again  dealt  with  in  the  chapters  on  generating 
plant  and  transmission  respectively. 

When  speaking  of  continuous  current  we  assume 
that  the  pressure  is  the  constant  or  maintained  voltage 
between  two  conductors,  or  between  one  conductor 
and  earth  ;  but  in  alternating  current  work  we  have 
no  such  constant  voltage,  as  the  latter  is  always 
varying  between  zero  and  a  maximum,  and  also 
constantly  changing  its  direction  or  sign  ;  we  have 
therefore  no  positive  or  negative  conductor,  since 
each  conductor  in  turn  is  alternately  positive  and 
negative. 

What  then  are  we  to  understand  by  voltage  in 
connexion  with  an  alternating  current  supply  ? 
If  the  terminals  of  such  a  supply  are  connected  to  an 
electrostatic,  or  a  hot  wire  voltmeter,  previously 
calibrated  for  continuous  current,  we  shall  find  that 
the  instrument  settles  down  to  a  reading  which  is 
an  average  of  the  pressure  wave.  Speaking  more 
correctly,  we  may  say  that  the  value  is  the  square 
root  of  the  mean  square  of  the  vertical  ordinates 
representing  pressure.  This,  however,  need  not 


GENERAL  PRINCIPLES  7 

trouble  the  reader,  because  we  shall  always,  in  future, 
refer  to  the  voltage  of  an  alternating  current  supply 
in  terms  of .  "  virtual  "  volts,  that  is,  the  average, 
or  root-mean-square  volts,  such  as  would  be  recorded 
on  an  electrostatic,  hot  wire  or  other  properly 
calibrated  instrument. 

The  same  remarks  hold  good  in  reference  to  amperes 
in  an  alternating  current  circuit,  and  we  shall  hence- 
forth refer  to  "  virtual  "  amperes  such  as  would  be 
recorded  on  a  hot  wire  or  other  type  of  properly 
calibrated  ammeter. 

It  is,  of  course,  obvious  that  we  cannot  measure 
alternating  pressure  or  current  on  continuous  cur- 
rent instruments  of  the  moving-coil  type,  which 
are  only  suitable  for  current  passing  in  a  certain 
direction.  Space  cannot  be  spared  to  enable  us 
to  enter  into  this  matter  in  greater  detail,  and  readers 
desiring  a  more  extensive  knowledge  of  alternating 
currents  in  theory,  will  be  able  to  obtain  same  from 
one  or  other  of  the  special  treatises  on  this  subject. 

Here,  we  are  only  concerned  with  the  practical 
application  of  electricity  to  mining  purposes :  but 
it  will  be  as  well,  for  the  sake  of  those  having  little 
practical  experience  of  alternating  currents  if  we 
clear  the  ground  somewhat  as  regards  the  application 
of  Ohm's  law  to  alternating  current  work. 

We  have  seen  that,  in  dealing  with  continuous 
currents,  the  relation  between  pressure,  current, 
and  resistance,  is  given  by  Ohm's  law.  This  law 
also  holds  good  for  alternating  currents,  but  is 
rather  complicated  by  a  factor  known  as  "  reactance." 
This  reactance  is  similar  in  effect  to  resistance, 
except  that  it  does  not  necessarily  involve  a  waste 
of  energy,  which  always  occurs  when  current  passes 
through  a  resistance. 

In  alternating  current  practice  we  have  to  take 
into  account  the  combined  effect  of  resistance  and 
reactance,  and  the  combination  is  technically  known 
as  impedance,  the  value  of  which  is  obtained  by 


8     ELECTRICAL  MINING  INSTALLATIONS 

taking  the  square  root  of  the  square  of  the  resistance, 
plus  the  square  of  the  reactance,  thus 

A/Res.2  +  React.2  =  impedance. 
With  this  modification,  Ohm's  law  then  becomes*  — 

E 
VRes.2  +  React.  2  =  C, 

E 
-=  x/Res2  +  React.2 


Res.2  +  React.2 

It  is  impossible  to  deal  further,  here,  with  the 
nature  of  reactance,  but  sufficient  has  been  said  to 
make  the  expression  clear,  and  the  matter  will  be 
referred  to  again  as  occasion  demands.  Suffice  it 
that  in  calculating  the  pressure  drop  in  cables  or 
transmission  wires,  the  reactance  will  not,  in  ordinary 
cases,  affect  the  result  to  any  practical  extent. 

Before  leaving  this  part  of  the  subject,  a  word 
must  be  said  regarding  power  in  alternating  current 
circuits.  We  already  know  that  power  in  a  con- 
tinuous current  system  is  represented  by  the  product 
of  volts  and  amperes  ;  but  this  is  not  necessarily 
true  in  regard  to  alternating  current  work. 

Referring  to  the  curves  shown  in  Pig.  1  (B)  it  will 
be  noted  that  the  current  and  pressure  are  "  in 
phase,"  that  is  to  say  they  each  pass  through  the 
zero  line  at  the  same  instant,  and  the  power  may  be 
obtained  by  multiplying  the  volts  and  amperes  at 
any  instant,  and  plotting  another  curve.  If  then 
an  average  be  taken  of  this  power  curve,  we  shall 
obtain  the  true  power,  which  is  exactly  the  same  as 
the  product  of  the  virtual  volts  and  virtual  amperes. 

The  pressure  and  current  curves  will  always  be  in 
phase  as  long  as  the  external  circuit  includes  resist- 
ance only  ;  but,  if  reactance  is  present,  the  current 
curve  will  lag  behind  the  pressure  curve  in  point 
of  time,  and  will  be  as  shown  in  Fig.  3.  In  actual 
practice  the  pressure  and  current  are  never  abso- 
lutely in  phase,  and  in  the  majority  of  cases,  where 


GENERAL  PRINCIPLES 


9 


motors  are  running  on  the  circuit,  the  current  may 
lag  very  considerably  behind  the  pressure. 

It  is  possible,  under  certain  circumstances,  that 
the  current  may  lead  in  phase,  but  as  this  very 
seldom  occurs  in  practice  we  need  not  deal  with  the 
matter  here. 


FIG.  3.     CURVE  SHOWING  PRESSURE  AND  LAGGING  CURRENT 
WITH  RESULTANT  POWER  CURVE. 

Referring  again  to  Fig.  3,  if  we  multiply  the  volts 
and  amperes  at  any  particular  instant  and  plot  a 
power  curve  we  find  that  at  times  there  exists  a 
positive  voltage  and  a  negative  current,  or  a  positive 
current  and  a  negative  voltage,  which  means  that 
at  such  times  we  have  negative  power,  and  the 
power  curve  will  be  as  shown.  If  we  take  the  average 
of  this  curve,  and  subtract  the  negative  from  the 
positive  part,  we  shall  find  that  the  result  is  con- 
siderably less  than  the  product  of  the  virtual  volts 
and  amperes. 

We  now  have  two  expressions  : — 

(a)  The  apparent  watts  obtained  by  multiplying 

the  volts  and  amperes. 

(b)  The  true  watts  obtained  from  the  curve. 
From    these   two    expressions   we    obtain    a   new 

ratio,  technically  known  as  "  power  factor." 

T»          £  TRUE   WATTS. 

Power  factor  =  — z — — 

APPARENT  WATTS. 

This  quantity  is  sometimes  referred  to  as  Cos.  </>, 


10  ELECTRICAL  MINING   INSTALLATIONS 

because  it  is  also  arrived  at  by  calculating  the  cosine 
of  the  angle  of  lag,  generally  known  by  the  Greek 
letter  <£. 

It  is  obvious,  from  the  above,  that  the  power 
factor  must  always  be  less  than  unity,  and,  as  a 
matter  of  fact,  the  following  average  values  may  be 
assumed  in  actual  practice  : — 

Incandescent  Lighting      .          .          .  -95 

Mixed  Lighting        .          •          .          .  -85 

Synchronous  machinery   .          .          .  -95 

Well  loaded  large  induction  motors  -85  to  -90 

Average  loaded  induction  motors       .  -70  to  -80 

Ditto  ditto  with  lighting  .          .  -75  to  -85 

Power  factor  is  also  sometimes  referred  to  as  a 
percentage,  thus  85  per  cent,  power  factor  =  -85. 

It  is  evident  from  the  foregoing  that  power  in  an 
alternating  current  system  can  be  calculated  from 
the  expression  : — 

Volts  x  Amperes  X  Power  factor  =  Watts. 

This  refers  particularly  to  single-phase  ;  and  the 
corresponding  expressions  for  two-phase  and  three- 
phase  working  are  as  follows  : — 

Two-phase  : — Volts  x  Amperes  x  Power  factor  X 
2  =  Watts. 

Three-phase  : — Volts  X  Amperes  x  Power  factor 
Xv/ 3  — Watts. 

This  matter  is  further  dealt  with  in  the  chapter 
entitled  "  Transmission,"  to  which  the  reader  is 
referred  for  further  particulars. 


CHAPTER   II 
GENERATING  PLANT 

THE  source  from  which  electrical  energy  has  to  be 
obtained  is  the  first  important  consideration.  In 
many  cases  it  so  happens  that  electricity  is  supplied 
in  a  district  by  one  of  the  modern  electric  power 
companies,  which  have  sprung  up  in  recent  years. 
These  concerns  can  often  supply  electricity  in  bulk, 
at  such  a  price  that  it  would  not  pay  the  colliery 
owner  to  generate  on  his  own  account  and,  if  suitable 
terms  can  be  arranged,  it  may  be  good  policy  to  take 
such  supply  in  bulk  instead  of  erecting  a  private 
generating  station. 

Before  deciding,  many  considerations  will  have 
to  be  taken  into  account,  and  the  actual  cost  of 
electrical  energy  may  not  be  the  predominating 
factor.  One  great  advantage  should  be  the  saving 
in  capital  expenditure,  and  the  interest  and  sinking 
fund  charges  thereon,  as  well  as  maintenance  and 
supervision  costs. 

In  many  parts  of  the  country  at  present,  no  such 
bulk  supply  is  available,  and  local  colliery  owners 
have  no  option  but  to  purchase  plant,  and  erect 
their  own  generating  station.  It  must  be  admitted 
that,  in  the  majority  of  moderate  and  large  installa- 
tions, this  course  is  entirely  warranted,  because 
plant  may  be  put  down  of  a  type  best  suited  to  the 
requirements  of  the  case,  and  the  generating  costs 
(taking  everything  into  consideration)  thus  reduced 


12  ELECTRICAL  MINING  INSTALLATIONS 

to  a  figure  which  will  compare  favourably  with  that 
charged  by  bulk  supply  authorities. 

Having  decided  that  the  colliery  is  to  be  equipped 
with  its  own  electric  generating  station,  we  are 
confronted  with  an  almost  endless  variety  of  systems 
and  types  of  plant,  suitable  for  the  purpose. 

Fuel  may  be  burnt  under  boilers,  and  steam  gene- 
rated, for  conversion  into  mechanical  power  by 
steam  engines  or  steam  turbines ;  or,  where  the 
coal  is  of  the  coking  variety,  we  can  employ  gas 
engines  and  utilize  the  coke  oven  gas. 

Large  gas  engines  have  not  hitherto  found  favour 
in  this  country,  although  used  extensively  on  the 
Continent,  but  there  is  now  every  indication  that 
the  adoption  of  such  plants  for  colliery  purposes 
is  being  seriously  considered,  and  several  plants 
have  already  been  put  down. 

It  is  a  remarkable  fact  that,  whereas,  years  ago, 
colliery  plants  were  worked  on  most  uneconomical 
lines  (so  far  as  fuel  consumption  is  concerned),  at 
present  great  attention  is  given  to  this  branch  of 
the  subject,  and  all  the  latest  and  most  modern 
improvements  adopted  to  reduce  fuel  consumption 
to  a  minimum. 

The  older  installations  were  worked  at  a  low 
steam  pressure,  with  a  long  range  of  steam  pipes, 
together  with  inefficient  engines  and  auxiliaries, 
but  we  now  find  the  most  up-to-date  boilers,  working 
at  high  pressure,  with  economizers,  superheaters, 
scientifically-designed  steam  range,  triple-expansion 
engines  with  low  steam  consumption,  condensing 
plants,  and  electrically-driven  auxiliaries ;  all  of 
which  tend  to  reduce  the  fuel  costs,  per  unit  generated, 
to  the  lowest  possible  value. 

This  is  especially  necessary  when  the  coal  is  of 
good  quality,  and  for  which  a  high  price  can  be 
obtained  in  the  market.  On  the  other  hand,  some 
coal  brought  to  the  surface  may  be  of  very  low 
grade,  and  here  again  we  find  that  boiler  furnaces 


GENERATING  PLANT  13 

have  been  so  improved,  that,  in  conjunction  with 
forced  draught,  this  class  of  fuel  may  be  utilized 
for  raising  steam,  instead  of  being  consigned  to  the 
waste  heap  because  it  has  no  market  value. 

Further,  we  notice  that  colliery  installations  now 
include  the  most  modern  and  up-to-date  appliances 
in  boilerhouse  plant,  e.g.,  mechanical  stokers,  coal 
and  ash  conveyors,  and  similar  labour-saving  devices, 
all  designed  to  reduce  operating  costs. 

We  need  not  enter  into  further  detail  in  regard 
to  the  design  of  boilerhouse  plant,  as  the  question 
does  not  lie  directly  within  the  scope  of  this  volume  ; 
and  the  next  matter  to  engage  our  attention  is  the 
engine,  or  prime  mover. 

In  regard  to  steam  engines,  present  day  tendency 
in  colliery  power  stations  is  to  emulate  the  example 
of  the  public  supply  authority,  and  adopt  high- 
speed, vertical,  enclosed  engines,  or,  in  some  cases, 
steam  turbines.  It  has  been  proved  that  this  class 
of  engine  is  entirely  suited  to  the  somewhat  trying 
conditions  of  colliery  service  whilst  their  efficiency 
is  high  ;  at  the  same  time  the  small  floor  area  occu- 
pied by  these  high-speed  sets  is  a  great  advantage 
where  space  is  limited. 

Colliery  men  in  the  past,  however,  could  not  get 
away  from  the  class  of  engine  to  which  they  had  been 
accustomed,  viz.,  the  slow  speed,  horizontal  type, 
as  used  for  winding,  etc.,  and  some  of  the  earlier 
installations  still  include  electric  generators  driven 
by  ropes  or  belts  from  such  slow-speed  horizontal 
engines.  There  is  no  doubt,  however,  that  in  nearly 
all  modern  colliery  power  stations,  the  high-speed, 
enclosed,  vertical  engine  has  found  its  place,  and 
proved  eminently  suitable  for  the  work. 

Coming  now  to  electric  generating  plant,  one  of 
two  systems  is  generally  employed,  namely  the 
continuous-current,  or  the  three-phase  alternating 
current  system. 

The  various  power  companies  supplying  electrical 


14  ELECTRICAL   MINING  INSTALLATIONS 

energy  in  bulk  in  this  country,  have  all  adopted  the 
high-tension,  alternating-current  system,  and  this 
is  practically  the  only  one  under  which  power  can 
be  efficiently  transmitted  over  great  distances.  If, 
then,  it  be  decided  to  purchase  electrical  energy 
in  bulk  from  such  a  source,  the  conditions  of  supply 
are  fixed,  although  the  pressure  may  be  transformed 
down,  to  any  suitable  value,  for  distribution  to 
motors,  etc.  Such  a  supply  can  also  be  converted 
into  continuous  current  by  means  of  rotary  con- 
verters or  motor-generators  if  necessary. 

In  the  event  of  a  colliery  company  deciding  to 
put  down  their  own  generating  station,  it  is  open 
for  them  to  adopt  continuous  or  alternating  current 
supply,  and  this  brings  us  to  the  question  of  the 
relative  advantages  of  the  two  systems  for  mining 
work. 

This  question  has  practically  resolved  itself  in 
favour  of  the  three-phase  alternating-current  system, 
although,  as  before  stated,  continuous  current  may 
suffice  for  small  installations  where  the  distances  to 
be  covered  are  comparatively  small,  and  the  conditions 
not  severe. 

It  is,  perhaps,  not  surprising  that  the  three-phase 
alternating-current  system  should  have  found  such 
favour,  because,  in  addition  to  the  efficient  distri- 
bution of  energy  over  great  distances,  and  the  ease 
with  which  the  pressure  may  be  transformed  from 
high  into  low  tension  as  required,  three-phase  motors 
themselves  possess  several  advantages  over  continuous- 
current  machines.  For  instance,  three-phase  motors 
of  the  short-circuited  rotor  type,  represent  the 
simplest  possible  construction,  having  no  commutator 
or  rubbing  contacts  whatever,  nor  complicated 
starting  gear.  In  fact,  for  small  machines,  no 
starting  gear  is  required,  other  than  the  usual  three- 
pole  switch,  and  such  a  machine  will  start,  and  run 
up  to  speed,  with  a  current  equal  to  about  three  times 
the  normal.  Then  again,  the  cost  is  much  less  than 


GENERATING  PLANT  15 

that  of  a  corresponding  continuous-current  motor 
with  its  attendant  starting  gear. 

Three-phase  motors,  with  wound  rotors  and  slip 
rings,  have  advantages  over  continuous-current 
machines,  in  the  absence  of  commutator  and  sparking 
troubles,  and  the  constant  attention  necessary  to 
keep  a  continuous-current  machine  in  working  order. 
Three-phase  machines  are  better  mechanically,  and 
there  is  less  likelihood  of  breakdown  ;  consequently 
the  cost  of  repairs  and  maintenance  is  much  smaller. 

One  important  point  must  not  be  overlooked, 
viz.,  the  fire  risk,  which  is  a  minimum  with  three- 
phase  motors,  owing  to  the  absence  of  a  commutator. 

Apart  from  motors,  the  three-phase  alternating- 
current  system  has  great  advantages  from  the  power 
distribution  standpoint.  For  instance,  a  three- 
core,  three-phase,  armoured  cable,  down  the  shaft 
or  in  the  roads,  makes  a  much  better  Job  than  two 
continuous-current  conductors,  while  the  cost  of 
such  a  cable,  for  a  given  pressure,  is  usually  less. 

On  the  other  hand,  it  must  be  admitted  that, 
for  a  certain  class  of  duty,  continuous  current  has 
the  advantage,  particularly  in  regard  to  traction  by 
locomotives,  in  connexion  with  which  continuous- 
current  motors  are  practically  indispensable,  but  as 
there  has  been  little  demand  in  this  country  for  such 
service  this  argument  carries  little  weight. 

For  a  long  time  there  seems  to  have  been  a  deep- 
rooted  objection  to  the  use  of  three-phase  motors 
for  coal  cutters,  and  at  one  period  it  was  considered 
necessary  to  employ  continuous-current  machines 
for  this  work,  but,  with  improvements  in  three-phase 
motors  for  this  purpose,  coal  cutters  are  being  adopted 
on  alternating-current  systems  with  complete  success. 

It  is  unnecessary  to  enlarge  upon  continuous- 
current  generating  plant,  except  perhaps  to  add 
that  machines  should  be  compound  wound,  to 
secure  an  increase  in  pressure  between  no  load  and 
full  load.  Continuous-current  generators  for  mining 


16  ELECTRICAL  MINING  INSTALLATIONS 

work  should  also  be  capable  of  withstanding  con- 
siderable overloads  without  sparking  or  damage. 
Most  firms  manufacturing  this  class  of  plant  now 
provide  machines  with  interpoles,  which  automatically 
compensate  for  armature  reaction,  and  enable  the 
sets  to  withstand  very  considerable  overloads  with- 
out sparking  or  need  for  altering  the  position  of 
the  brushes  ;  in  many  cases  the  position  of  the 
brushes  is  permanently  fixed  and  no  facilities  are 
provided  for  adjustment  after  the  machine  has  left 
the  makers'  works. 

The  diagram,  Pig.   4,  shows  internal  connexions 


FIG.  4.     DIAGRAM  OF  CONNEXIONS  FOB  COMPOUND  WOUND 
INTERPOLE  GENERATOR. 

of  a  multipolar,  compound  wound,  generator  with 
interpoles. 

With  regard  to  A.C.  machines,  these  are  usually 
of  the  stationary  armature  type,  with  revolving 
fields,  the  necessary  excitation  being  provided  from 
some  external  source,  as  an  alternator  cannot  be 
self -exciting  like  a  continuous-current  machine. 

The  exciter  consists  of  a  continuous-current  gene- 


GENERATING  PLANT 


17 


rator    of   comparatively   low    voltage,    often    direct 
coupled  to  the  alternator  shaft,  and  driven  by  the 


St3r  Connection 


b  r 


Mesh  Connection 


Neutral  Wire 


Star  Connection  with  Neutral  for  Lighting 


FIG.  5.     CONNEXIONS  FOB  THREE-PHASE  WINDINGS. 

same  engine,  but  continuous  current  from  any  suit- 
able external  source  can  be  employed  for  magnetizing 

0 


18   ELECTRICAL  MINING  INSTALLATIONS 

the  revolving  field  of  the  alternating  current  machine. 

As  already  explained,  the  armature  windings  of 
two-phase  or  three-phase  machines  really  consist 
of  two  or  three  separate  single-phase  windings  so 
placed  as  to  give  a  different  phase  relation  between 
the  individual  circuits  as  shown  in  Pig.  2.  There 
are,  however,  two  distinct  methods  of  coupling  up 
the  windings  for  a  three-phase  supply,  known  tech- 
nically, as  "  star  "  and  "  mesh  "  (or  delta,  as  the 
latter  is  sometimes  called,  because  the  arrangement 
takes  the  form  of  a  triangle,  the  Greek  letter  "  A  "). 
Fig.  5  will  make  this  clear. 

In  referring  to  the  voltage  of  a  three-phase  system, 
we  always  understand  the  pressure  between  lines, 
i.e.  between  a  and  6,  a  and  c,  or  b  and  c,  which  are,  or 
should  be,  equal. 

It  will  be  obvious  from  the  diagram  that  if  each 
of  the  three  single-phase  windings  gives  a  certain 
voltage,  X,  the  pressure  between  the  outgoing  lines 
will  depend  upon  the  arrangement  of  connexions 
adopted.  If  X  represent  the  voltage,  and  Y,  the 
current,  of  each  single-phase  winding,  then  the 
resultant  voltage  and  current  of  the  three-phase 
system  will  be  as  follows  : — 

(a)  Star  connexion  :  Volts  between  lines  =X  X  V3 

Current  in  each  line  =  Y. 

(b)  Mesh    connexion  :    Volts    between   lines  =  X. 

Current  in  each  line  =  Y  X  \/3 
Thus  the  result,  so  far  as  power  is  concerned,    is 
the  same  in  each  case,  but  each  method  has  its  advan- 
tages or  disadvantages,  more  particularly  as  regards 
external  conditions. 

Three-phase  motors  may  be  connected,  "  star " 
or  "  mesh,"  in  the  same  way  as  alternators,  and 
all  such  motors  are  provided  with  three  terminals, 
to  which  corresponding  lines  of  the  three-phase 
system  are  connected. 

In  mining  practice  it  is  customary  to  earth  some 
point  of  the  system,  and  with  the  "  star  "  connected 


GENERATING  PLANT  19 

alternator  this  is  usually  the  centre  or  neutral 
point ;  in  "  mesh  "  connected  machines  it  is  usual 
to  dispense  with  earth  connexions  but  one  or  other 
of  the  junctions  of  the  phases  may  be  temporarily 
earthed  for  testing  purposes  as  shown  in  the  diagram. 

If  the  alternating-current  generators  are  also 
required  to  provide  the  power  necessary  for  lighting 
it  is  usual  to  adopt  the  "  star  "  system  of  connexion 
and  also  to  run  out  an  additional  conductor  from  a 
neutral  point  as  shown  in  Fig.  5  C,  in  which  case  the 
lighting  load  is  connected  between  the  neutral  wire 
and  each  line,  care  being  taken  to  divide  it  uniformly 
between  the  three  phases.  With  this  arrangement  of 
connexions  the  lighting  pressure  is  only  equal  to 
that  between  the  lines,  divided  by  \/3  (1-73  approxi- 
mately) so  that,  to  assume  a  case,  the  pressure  for 
motors  may  be  400  volts  between  the  lines,  and  that 
for  lighting,  230  volts  between  neutral  and  each  line 
wire. 

It  is  not,  of  course,  absolutely  necessary  to  balance 
the  lighting  on  each  phase,  exactly,  although  this 
should  be  done  as  far  as  possible.  In  the  event  of 
unequal  balancing  the  out-of-balance  current  returns 
through  the  neutral  wire. 

In  alternating-current  generators  we  have  another 
factor  to  deal  with, namely  " frequency,"  or  "period- 
icity," recorded  in  cycles  per  second.  As  explained  pre- 
viously, this  frequency  is  usually  50  cycles  per  second 
for  lighting,  or  for  mixed  lighting  and  general  power 
work,  and  25  cycles  per  second  for  large  power 
systems  only.  The  frequency  for  any  particular 
machine  is  given  by  the  formula  : — Number  of  pairs 
of  poles  x  R.P.M.  -f-  60. 

From  this  it  will  be  seen  that  as  the  number  of 
pairs  of  poles  must  be  some  whole  number  (without 
a  fraction)  we  are  limited  to  certain  definite  speeds 
in  order  to  obtain  standard  frequencies.  For  in- 
stance, a  50  cycle  generator  for  direct  coupling  to  a 
high-speed  engine  must  run  a-t  300,  333,  375,  428, 


20   ELECTRICAL  MINING  INSTALLATIONS 

500,  etc.,  revolutions  per  minute,  and  no  intermediate 
speeds  are  possible.  For  the  same  reason,  in  a  25 
cycle  generator  the  speeds  are  even  more  restricted, 
and  we  have  to  choose  between  300,  375,  500,  etc., 
revolutions  per  minute. 

There  is  one  other  point  in  regard  to  the  output 
or  capacity  of  alternating-current  generators,  which 
is  perhaps  not  thoroughly  understood  and  appreciated 
by  all  engineers.  This  is  the  power  factor  referred 
to  in  a  previous  chapter. 

We  have  already  seen,  that,  provided  there  is  no 
lag  or  phase  difference  between  the  pressure  and 
current  curves,  the  power  in  any  three-phase  alter- 
nating-current circuit  is  given  by  the  expression  : 
Volts  X  Amperes  X  A/3  =  Watts,  but  when  con- 
ditions are  present  which  cause  a  lag  or  phase  differ- 
ence, the  power  is  less  than  it  otherwise  would  have 
been,  as  shown  by  the  expression  : 

Volts  X  Amperes  x  \/3  X  Power  factor  =  Watts. 

In  any  three-phase  alternating-current  generator, 
the  voltage  and  current  are  fixed,  and  these,  together 
with  the  speed,  determine  the  size  of  the  machine, 
but  the  actual  output  in  true  watts  or  kilowatts 
will  depend  upon  external  conditions,  which  must 
be  known  before  the  capacity  of  such  a  machine 
can  be  specified. 

In  a  previous  chapter  a  table  of  probable  power 
factor  values  has  been  given  for  different  classes  of 
work. 

This  question  of  power  factor  has  another  effect 
on  the  performance  of  the  machine.  All  electric 
generators  are  subject  to  a  decrease  in  pressure  as 
the  load  increases,  unless  this  is  compensated  for 
by  a  compound  winding,  or  by  interpoles,  as  on 
continuous-current  machines.  No  such  satisfactory 
method  has  been  found  to  yield  similar  results  on 
alternating-current  machines,  and  we  therefore 
have  to  face  the  fact  that  the  latter,  working  under 
conditions  of  constant  speed  arid  excitation,  have  an 


GENERATING  PLANT  21 

inherent  tendency  towards  loss  in  pressure  as  the 
load  comes  on. 

With  machines  supplying  a  lighting  or  non-inductive 
load,  where  there  is  no  appreciable  lag  between 
pressure  and  current,  and  where  the  power  factor  is 
consequently  equal  to  unity,  this  decrease  in  pressure, 
or  "  pressure  drop,"  will  be  in  the  neighbourhood 
of  5  per  cent,  to  7  per  cent.,  but  the  same  machine 
supplying  an  inductive  load,  with  a  power  factor  of 
say,  '8,  will  have  a  corresponding  pressure  drop  of 
the  order  of  14  per  cent,  to  20  per  cent.  The  exact 
value  will  depend  entirely  upon  the  characteristic 
of  the  machine  in  question. 

In  giving  these  figures  for  pressure  drop  it  is  of- 
course  assumed  that  the  speed  and  excitation  remain 
constant,  for  it  is  obvious  that  the  pressure  may  be 
varied  by  altering  the  excitation,  and,  in  practice, 
the  excitation  would  be  altered  by  means  of  the 
field  regulating  resistance,  to  compensate  for  the 
fall  in  pressure.  By  this  means  the  pressure  can 
be  maintained  constant,  provided  that  some  one  is  in 
attendance,  to  adjust  the  field  regulating  resistance 
to  suit  the  requirements  of  the  load. 

Various  automatic  devices  have  been  brought 
out  from  time  to  time,  for  automatically  varying  the 
excitation  to  keep  the  pressure  constant  under  all 
conditions. 

The  power  required  to  drive  any  electric  generator 
when  the  output  in  kilowatts  is  known,  is  given  by 
the  formula  :  — 


B.H.P.  =  -r-  Efficiency. 


When  the  efficiency  is  expressed  as  percentage,  we 
divide  it  by  100.  For  instance,  if  we  require  to 
know  the  power  necessary  to  drive  a  100  k.w.  (that 
is  100  X  1000  watts)  generator  having  an  efficiency 
of  89  -5  per  cent,  at  full  load,  we  obtain  :  — 

100,000  Watts  .    89-5__  ,  -A  ^  TT  T> 
-—-     -^-^allDIULF. 


22    ELECTRICAL  MINING  INSTALLATIONS 

From  this  it  will  be  seen  that  the  horse-power  re- 
quired, is  equal  to  about  1£  times  the  kilowatt 
capacity  of  the  machine,  and  this  approximate 
rule  will  often  prove  useful,  but  it  must  be  remem- 
bered that  the  horse-power  will  be  greater,  in  the 
case  of  small  machines  of  low  efficiency,  and  less 
with  large  machines  having  a  higher  efficiency. 

In  connexion  with  alternating-current  generators, 
we  often  come  across  the  expression  K.V.A.  or  kilo- 
volt-amperes,  i.e.,  the  product  of  volts  and  amperes, 
divided  by  1,000,  or  in  other  words  the  apparent 
kilowatts.  From  what  has  already  been  said  it 
follows  that,  by  multiplying  together  the  apparent 
kilowatts  and  the  power  factor,  we  obtain  the  true 
kilowatts,  and  it  must  be  mentioned  that,  when 
calculating  the  horse-power  required  to  drive  a 
generator,  we  must  always  take  the  true  and  not  the 
apparent  kilowatts  or  k.v.a.  output. 

Machines  are  often  referred  to  in  terms  of  their 
k.v.a.  capacity,  and  this  fixes  the  size  of  the  machine, 
but  at  the  same  time  conveys  no  idea  of  the  true 
output  in  kilowatts  in  any  particular  case,  or  the 
power  required  to  drive,  unless  we  know  the  power 
factor  of  the  circuit  which  the  machine  has  to  supply  ; 
obviously  the  machine  will  require  maximum  power 
to  drive  it  when  the  power  factor  is  highest,  viz., 
1-0,  in  which  case  the  kilowatt  output  is  equal  to 
the  k.v.a. 


CHAPTER   III 
GENERATING  STATION  SWITCHGEAR 

MUCH  might  be  written  on  the  subject  of  generating 
station  switchgear  for  mining  installations,  but  we 
must  confine  ourselves  to  general  principles  and  give 
details  only  so  far  as  they  lie  within  the  scope  of 
this  manual. 

In  the  first  place  special  conditions  have  to  be 
complied  with  in  the  Home  Office  rules,  the  salient 
features  being  embodied  in  the  following  abstract. 

"  There  shall  be  a  passage-way  in  front  of  the 
switchboard  of  not  less  than  3  ft.  in  width,  and  if 
there  are  any  connexions  at  the  back  of  the  switch- 
board, any  passage-way  behind  the  switchboard 
shall  not  be  less  than  3  ft.  clear.  This  space  shall 
not  be  utilized  as  a  store-room,  or  a  lumber-room,  or 
obstructed  in  any  manner  by  resistance  frames, 
meters,  or  otherwise.  If  space  is  required  for  resist- 
ance frames  or  other  electrical  apparatus  behind 
the  board,  the  passage-way  must  be  widened  accord- 
ingly. No  cable  shall  cross  the  passage-way  at  the 
back  of  the  board  except  below  the  floor,  or  at  a 
height  of  not  less  than  7  ft.  above  the  floor. 

"  The  space  at  the  switchboards  shall  be  properly 
floored,  accessible  from  each  end,  and,  except  in 
the  case  of  low  pressure  switchboards,  must  be  kept 
locked,  but  the  lock  must  allow  of  the  door  being 
opened  from  the  inside  without  use  of  a  key.  The 
floor  at  the  back  shall  be  incombustible,  firm,  and 
even. 


24  ELECTRICAL  MINING  INSTALLATIONS 

"  Every  generator  shall  be  provided  with  a  switch 
on  each  pole,  between  the  generator  and  the  busbars. 

"  Where  continuous-current  generators  are  paralleled 
reverse  current  cutouts  shall  be  provided. 

"  Suitable  instruments  shall  be  provided  for 
measuring  the  current  and  pressure  of  each  generator. 

"  Every  feeder  circuit  shall  at  its  origin  be  pro- 
vided with  an  ammeter. 

"  If  the  transmission  lines  from  the  generating 
station  to  the  pit  are  overhead  there  shall  be  lightning 
arresters  in  connexion  with  the  feeder  circuits. 

"  Automatic  cutouts  must  be  so  arranged  that, 
when  the  contact  lever  opens  outwards,  no  danger 
exists  of  striking  the  head  of  the  attendant.  If 
unenclosed  fuses  are  used  they  must  be  placed  within 
2  ft.  of  the  floor,  or  be  otherwise  suitably  protected.. 

"  Where  the  supply  is  at  a  pressure  exceeding  the 
limits  of  medium  pressure,  there  shall  be  no  live; 
metal  work  on  the  front  of  the  main  switchboard 
within  8  ft.  of  the  floor  or  platform,  and  the  space 
provided  under  Rule  2  of  this  section  shall  be  not 
less  than  4  ft.  in  the  clear.  Insulating  floors  or 
mats  shall  be  provided  for  medium  pressure  boards 
where  live  metal  work  is  on  the  front  or  back. 

"  All  terminals  and  live  metal  on  machines  over 
medium  pressure  above  ground,  and  over  low  pressure 
under  ground,  shall,  where  practicable,  be  protected 
with  insulating  covers,  or  with  metal  covers  con- 
nected to  earth. 

"  The  insulation  of  every  complete  circuit,  other 
than  telephone  or  signal  wires,  used  for  the  supply 
of  energy,  including  all  machinery,  apparatus,  and 
devices  forming  part  of,  or  in  connexion  with  such 
circuit,  shall  be  so  maintained  that  the  leakage 
current  shall,  so  far  as  is  reasonably  practicable , 
not  exceed  yoVo-  °f  the  maximum  supply  current 
and  suitable  means  shall  be  provided  for  the  imme- 
diate localization  of  leakage. 

"  In  every  completely  insulated  circuit,  earth  or' 


GENERATING  STATION  SWITCHGEAR    25 

fault  detectors  shall  be  kept  connected  up,  in  every 
generating  and  transforming  station,  to  show,  imme- 
diately, any  defect  in  the  insulation  of  the  system. 
The  readings  of  these  instruments  shall  be  recorded 
daily  in  a  book  kept  at  the  generating  or  transforming 
station,  or  switch-house. 

"  Main  and  distribution  switch  and  fuse  boards 
must  be  of  incombustible  insulating  material,  such 
as  marble  or  slate,  free  from  metallic  veins,  and 
be  fixed  in  as  dry  a  situation  as  practicable. 

"Every  sub-circuit  must  be  protected  by  a  fuse 
on  each  pole.  Every  circuit  carrying  more  than  5 
amperes  up  to  125  volts  or  3  amperes  at  any  pressure 
above  125  volts  must  be  protected  in  one  of  the 
following  alternative  methods  : — 

(a)  By  an  automatic  maximum  cutout  on  each 

pole. 

(b)  By  a  detachable  fuse  on  each  pole,  constructed 

in  such  manner  that  it  can  be  removed 
from  a  live  circuit  with  the  minimum  risk  of 
shock. 

(c)  By  a  switch  and  fuse  on  each  pole." 

Dealing,  first  with  continuous-current  boards 
it  will  be  seen  that  the  pressure  would  in  practically 
all  cases  lie  between  250  and  650  volts,  such  installa- 
tions coming  under  the  heading  of  medium  pressure 
supply. 

Fig.  6  is  a  typical  diagram  of  connexions  of  a 
continuous-current  generating  station  switchboard, 
with  two  or  more  compound-wound  generators  and 
several  feeder  circuits.  Such  boards  are  usually 
constructed  of  plain  or  enamelled  slate,  in  a  wrought- 
iron  frame,  with  the  switching  apparatus  and  instru- 
ments mounted  on  the  front  of  the  panels,  the  back 
of  the  board  being  utilized  for  busbars,  connexions, 
instrument  shunts,  regulating  resistances,  etc.  Owing 
to  the  simple,  nature  of  the  general  lay-out,  and 
•construction,  an  illustration  showing  the  details 


26  ELECTRICAL  MINING  INSTALLATIONS 

of   continuous-current   boards   is    unnecessary,   the 
general  features  of  such  being  familiar  to  all. 

The  apparatus  on  the  panels  of  a  typical  switch- 
board controlling  shunt-wound  generators  may  be 
detailed  as  follows  : — 

Each  Generator  Panel  contains — 

One  amperemeter,  preferably  dead-beat,  moving- 
coil  pattern. 


FIG.  G.     DIAGRAM  OF  CONNEXIONS   FOB    CONTINUOUS  CUR- 
BENT   SWITCHBOABDS. 


One  single-pole,   overload  and  reverse    current 
automatic   circuit    breaker   on   positive   pole. 
One  single-pole  switch  on  negative  pole. 
One  single-pole  fuse  on  negative  pole. 
One  shunt  field  regulating  rheostat. 
One    field-breaking    switch    and    non-inductive 

resistance. 

One  set  of  paralleling  sockets  and  plug. 
Common  to  all  generator  panels  there  should  be 
a   main    busbar    voltmeter    (usually    mounted    over 
the  centre  of  the  complete  board) ;  also  one  paralleling 


GENERATING  STATION  SWITCHGEAR    27 

voltmeter  which  can  be  connected  to  the  paralleling 
sockets,  so  that  the  voltage  of  the  incoming  machine 
may  be  adjusted  before  switching  it  into  parallel 
with  the  running  machines.  Sometimes  this  parallel- 
ing voltmeter  is  mounted  on  a  swinging  bracket, 
at  one  end  of  the  board,  so  as  to  be  distinctly  visible 
to  the  switchboard  attendant. 
Each  Feeder  Panel  contains — 

One  amperemeter,  preferably  of  the  dead-beat, 
moving-coil  type. 

One  double-pole  switch. 

Two  single-pole  fuses. 

This  is,  perhaps,  the  simplest  possible  form  of 
board,  and  there  is  practically  no  end  to  the  elabora- 
tion and  refinements  that  could  be  added  if  desired. 
For  instance,  double-pole  circuit  breakers  are  some- 
times placed  on  the  generator  panels  as  shown  in 
Pig.  6  with  or  without  switches,  but,  as  most  double- 
pole  circuit  breakers  can  also  be  used  as  main  switches, 
especially  if  they  are  of  the  loose  handle  type,  and 
cannot  be  held  on  in  the  event  of  a  persistent  fault, 
there  is  no  advantage  gained  by  using  switches  in 
addition. 

With  compound  wound  machines  equalizing  switches 
will  be  necessary,  and  these  usually  take  the  form 
of  a  single-pole  switch,  placed  on  the  board,  in 
which  case  an  equalizing  busbar  will  have  to  be 
provided ;  or  the  equalizing  switches  may  be  placed 
on  the  machines  themselves.  It  will  be  at  once 
apparent  from  the  diagram  that  there  is  a  great 
saving  of  cable  in  adopting  this  latter  method,  and, 
as  the  equalizing  cable  is  of  substantial  section  there 
will  be  a  considerable  saving  in  cost. 

Coming  now  to  three-phase  alternating  current 
switchgear,  we  have  boards  for  medium  pressure, 
where  the  voltage  lies  between  250  and  650  volts ; 
and  also  boards  for  high-pressure,  where  the  voltage 
exceeds  the  latter  figure  but  does  not  exceed  3,000 
volts. 


28  ELECTRICAL  MINING  INSTALLATIONS 

The  following  remarks  will  also  apply  generally  to 
extra  high  pressure  switchgear,  but  such  schemes 
are  rarely  necessary  for  mining  installations  and 
we  need  not  specially  consider  them. 

Fig.  7  is  a  typical  diagram  of  connexions  for 
a  three-phase  generating  station  switchboard,  and 
will  apply  generally  to  both  medium  and  high- 


FIG.  7.     DIAGRAM    OF     CONNEXIONS 
SWITCHBOARD. 


FOR     THREE-PHASE 


pressure  installations.     The  apparatus  on  the  various 
panels  may  be  detailed  as  follows  : — 
Each  Generator  Panel  contains — 

One  triple-pole  oil  break  switch,  fitted  with 
alternating  current  instantaneous  overload 
trip  coils  in  two  phases. 

Two  current  transformers  for  operating  trip  coils. 
One  amperemeter  (probably  operated  from  one 

of  the  above  transformers). 
One  main  field  regulating  rheostat  for  alternator. 
The  necessary  synchronizing  plugs  and  sockets. 
Each  Exciter  Panel  contains — 
One  double-pole  switch, 
Two  single-pole  fuses. 


GENERATING  STATION  SWITCHGEAR    29 

One  exciter  amperemeter. 
One  shunt  regulating  rheostat. 
Each  Feeder  Panel  contains — 

One  triple-pole,  oil  break  switch,  fitted  with 
alternating-current  instantaneous  overload  trip 
coils  in  two  phases. 

Two  current  transformers  for  operating  trip  coils. 
One  amperemeter  (probably  operated  from  one 

of  the  above  transformers). 

A  main  busbar  voltmeter  will  also  be  necessary, 
and  may  be  placed  over  the  centre  of   the   board. 
In  addition,  a  paralleling  or  synchronizing!  voltmeter 
will  be  required,  this  being  connected  to  the  synchron- 
izing busbars  as  shown. 

For  important  boards  a  synchronizer  might  also 
be  fitted,  such  an  instrument  showing  at  a  glance 
whether  the  incoming  machine  is  running  too  fast 
or  too  slow.  This  apparatus  is  not,  however,  abso- 
lutely necessary,  and  is  often  omitted.  In  any  case 
it  is  usual  to  have  synchronizing  lamps,  so  that  the 
engine  driver,  and  switchboard  attendant,  can  tell 
when  the  incoming  machine  is  in  phase  with  those 
already  running. 

The  triple-pole  oil  break  switch  should  preferably 
have  a  free  handle  attachment,  so  that  it  is  impos- 
sible for  any  one  to  hold  this  on  while  a  persistent 
fault  exists.  The  switches  referred  to  above  have 
two  trip  coils,  but  obviously  one,  two,  or  three 
trip  coils~can  be  fitted  as  required.  The  general  rule 
is  to  use  two  ;  this  arrangement  gives  protection 
against  overload  in  all  three  phases,  because  the 
current  in  the  unprotected  phase  cannot  build  up 
without  also  increasing  the  current  in  the  other  two. 
When  generators  are  supplying  a  lighting  system, 
with  a  neutral  conductor,  or  when  the  neutral  is 
permanently  ^earthed,  it  is  preferable  to  fit  three 
trip  coils  on  the  main  generating-station  feeder 
switches. 
Alternating -current,  instantaneous  trip  coils,  are 


30    ELECTRICAL  MINING  INSTALLATIONS 

in  series  with  the  circuit  they  are  required  to  protect, 
and  may  be  direct  connected  in  the  case  of  a  medium 
pressure  board,  but  it  is  more  usual  to  employ  series 
transformers.  Such  transformers  are  absolutely  neces- 
sary in  the  case  of  high  pressure  boards,  in  order  to 
eliminate  all  high  pressure  parts  from  the  front  of 
the  panels,  and  they  are  often  employed  for  medium 
pressure  boards,  partly  because  it  enables  better 
arrangement  of  the  main  current  busbars  and  con- 
nexions behind  the  panels. 

The  same  remarks  apply  to  the  amperemeters, 
which  may  be  operated  from  one  of  the  trip  coil 
transformers  if  desired,  although,  for  various  reasons, 
it  is  sometimes  preferable  to  instal  independent 
transformers  for  the  purpose. 

Voltmeters  will,  in  the  case  of  medium  pressure 
boards,  be  connected  across  the  main  busbars,  but 
for  high  pressure  boards  potential  transformers 
wih1  be  necessary  ;  all  instruments  on  the  face  of 
the*;board  operating  on  low-tension  current. 

A  main  field-regulating  resistance  has  been  men- 
tioned for  the  alternator,  and  a  shunt  regulating 
resistance  for  the  exciter  fields,  but  here,  again, 
one  or  other  regulator  may  be  employed  alone, 
unless  it  is  required  to  utilize  the  exciter  circuit  for 
other  purposes  such  as  lighting,  in  which  case  both 
will  be  necessary. 

Since  the  general  construction  of  the  three-phase 
board  is  quite  special,  and  very  different  from  that 
of  a  continuous-current  board,  it  will  be  as  well 
to  illustrate  the  arrangement,  and  Fig.  8  repre- 
sents a  section  through  a  typical  generator  panel ; 
it  must  however  be  understood  that  arrangements 
differ  very  widely,  according  to  local  requirements, 
and  the  space  available. 

The  panels  for  three-phase  boards  are  usually 
of  polished  white  marble,  mounted  in  an  iron  frame, 
and  it  will  be  seen  from  the  illustration  that  con- 
siderable depth  is  necessary  to  accommodate  the 


GENERATING  STATION  SWITCHGEAR    31 


apparatus.  The  illustration  applies  more  particu- 
larly to  a  high-pressure  board  of  which  the  panels 
contain  low-tension  apparatus  only,  series  and  pres- 
sure transformers  being  employed  in  all  cases,  and 
placed  in  fire-proof  compartments,  so  that,  in  the 
event  of  any  accident  arising,  the  switchboard 
attendant  may  be  quite  safe,  and  the  damage  con- 
fined to  one  particular  compartment. 

Section   Switches^  High  Pressure  Bus  Bars 

m 


Triple  Pole  (hand) 
Oil  Switch. 


-x^^xpanded  Metal  or 
l\  "Perforated Sheet 


Field  Regulating  Resistance\ 


m  Fuses  for  Pressure 
1  'Transformers 

LowPressureConnectiono  ^ 

(from  Current  &  Pressurvt 

Transformers)^ 


A 


Cable  Trench 
FIG.  8.     SECTION    THROUGH    THREE-PHASE    SWITCHBOARD. 

It  will  be  noticed  that  a  passage  way  is  provided 
between  the  board,  and  the  compartments  at  the 
back,  containing  the  high-tension  apparatus  ;  access 
to  this  passage  way  being  obtained  through  doors 
at  one  or  both  ends,  and,  according  to  regulation, 
the  doors  must  be  fitted  with  locks  which  can  only 
be  opened  with  a  key  from  the  outside,  but  are 
negotiable  from  the  inside,  without  a  key. 


32  ELECTRICAL  MINING  INSTALLATIONS 

On  high-tension  boards  it  is  also  necessary  to 
fit  isolating  or  section  switches.  These  usually 
take  the  form  of  copper  links,  and  are  not  required 
to  break  a  current,  which  should  always  be  first 
dealt  with  on  the  oil  switch  ;  they  are  merely  to 
isolate  any  particular  portion  of  the  board,  so  that 
alterations,  repairs,  cleaning,  or  inspection,  may  be 
carried  out  without  risk  or  shock.  In  some  cases 
isolating  switches  are  so  interlocked  with  the  doors 
leading  to  the  chambers  or  compartments  that  access 
to  these  compartments  cannot  be  obtained  until 
the  isolating  switch  has  been  opened,  and  conversely, 
that  the  isolating  switches  cannot  be  replaced  until 
the  compartment  is  again  closed. 

Nothing  has  been  said  about  fuses  for  three-phase 
alternating  current  boards,  and,  as  a  matter  of  fact, 
it  is  not  usual  to  fit  them  on  generating  station 
panels,  except,  perhaps,  on  lighting  and  small  feeder 
circuits,  while  for  high  pressure  boards,  fuses  of  any 
kind  are  rigidly  avoided. 

It  can  easily  be  shown  that  a  fuse  does  not  give 
the  required  protection  for  three-phase  work,  while 
at  the  same  time,  the  cost  of  fuses  is  equivalent  to 
that  of  automatic  trip  coils  fitted  to  the  main  oil 
switches.  In  the  first  place  a  fuse  cannot  be  depended 
upon  to  operate  with  absolute  certainty  at  any  pre- 
determined current  value,  and,  further,  it  can  only 
operate  to  the  accompaniment  of  more  or  less  noise, 
smoke,  and  flashing,  often  damaging  surrounding  fit- 
tings, and  causing  a  disturbance  generally.  Further, 
it  cannot  be  replaced  as  quickly  as  an  automatic 
oil  switch,  and  it  is  necessary  to  stock  replacements 
to  suit  every  type  and  capacity  of  fuse  fitted. 

In  addition  to  these  disabilities,  a  fuse  may  only 
blow  on  one  or  two  poles,  and  maintain  the  pressure 
on  part  of  the  system  when  it  should  be  discon- 
nected, whereas  an  automatic  oil  switch,  fitted  with 
one,  two,  or  three  trip  coils,  opens  all  phases  instantly 
when  the  current  reaches  a  predetermined  value,  and 


GENERATING  STATION  SWITCHGEAR  33 

what  is  more  important,  current  is  always  inter- 
rupted by  an  oil  switch  as  it  passes  through  zero, 
thereby  minimizing  the  possibility  of  dangerous 
pressure  rises,  and  lessening  the  resultant  strain 
upon  machinery,  cables,  etc. 

Automatic  trip  coils  on  the  oil  switch  are  ciapable 
of  adjustment,  so  that  the  switch  can  be  temporarily 
under  or  overset  if  required,  without  interfering 
with  the  supply. 

The  above  remarks  apply  generally  to  the  employ- 
ment of  fuses  on  all  three-phase  boards,  but  in  the 
case  of  high-tension  service  it  is  very  difficult  to 
design  a  satisfactory  high-tension  fuse  that  will 
fulfil  the  requirements,  and  operate  with  safety. 

So  far  we  have  only  considered  the  use  of  plain 
alternating-current  instantaneous-overload  trip  coils 
for  oil  switches,  but  it  may,  in  certain  cases,  be  advis- 
able to  operate  the  trip  coil  through  a  relay  of  the 
time  limit  overload  or  reverse-current  pattern. 
Time-limit  overload  relays  may  be  designed  to 
open  very  quickly  on  heavy  overloads,  but  maintain 
a  supply  in  the  case  of  moderate  overloads,  the  time 
varying  inversely  as  the  magnitude  of  the  overload 
on  the  system.  Reverse  current  relays  are  designed 
to  trip  the  oil  switch  in  the  event  of  a  current,  or 
more  correctly  speaking,  power  reversal. 

The  Home  Office  rules  insist  on  reverse  current 
cutouts  being  provided  where  continuous-current 
generators  are  paralleled,  but  such  cutouts  or  relays, 
working  in  conjunction  with  trip  coils  on  the  auto- 
matic switches,  are  often  provided  in  connexion 
with  three-phase  generators  running  in  parallel, 
the  relays  being  used  singly,  or  in  conjunction  with 
instantaneous  or  time-limit  overload  relays. 

It  is  unnecessary  to  enter  into  a  detailed  descrip- 
tion of  these  relays,  suffice  it  that  they  are  usually 
operated  from  series  pressure  transformers,  and 
provided  with  relay  contacts,  so  that  it  is  only  neces- 
sary to  fit  the  oil  switches  with  one  trip  coil  in  the 


34    ELECTRICAL  MINING  INSTALLATIONS 

relay  circuit,  this  being  energized  by  any  of  the  relays 
and  actuating  the  switch  in  the  event  of  an  overload 
or  reverse  current. 

Time  limit  relays  are  often  fitted  to  the  outgoing 
feeder  circuits,  and  a  switchboard  so  arranged  is  in 
accordance  with  the  best  modern  practice. 

On  three-phase  alternating-current  switchboards 
we  sometimes  find  power  factor  indicators,  idle 
current  amperemeters,  and  frequency  meters,  but 
these  instruments  are  not  absolutely  necessary  for 
the  general  run  of  mining  installations,  and 
they  represent  refinements  which  can  be  safely 
omitted. 

In  regard  to  both  continuous-current  and  alter- 
nating-current switchboards,  integrating  watt-hour- 
meters  will  probably  be  considered  necessary  to 
measure  the  output.  In  an  important  installation 
such  wattmeters  may  be  placed  on  each  generator 
or  feeder  panel,  but  in  other  cases,  wattmeters  in  the 
main  busbars,  between  generator  and  feeder  panels, 
which  thus  record  the  total  output  of  the  station, 
will  be  all  that  is  necessary. 

As  there  is  a  great  deal  of  misunderstanding  about 
types  of  wattmeters,  it  should  be  noted  that  an  inte- 
grating watt-hour-meter  is  an  instrument  similar  to 
a  house  service  meter,  which  measures  the  total  energy 
passed  through  it.  An  indicating  wattmeter  would 
merely  indicate  the  watts  passing  at  any  given  mo- 
ment, while  a  recording  wattmeter,  like  a  recording 
voltmeter  or  amperemeter,  gives  a  continuous  record 
in  the  form  of  an  ink  line  on  a  paper  chart,  showing 
the  actual  value  of  the  watts  in  the  circuit  over  a 
period.  Obviously  by  integrating  this  curve  we 
obtain  watt  hours,  such  as  would  be  measured  by  an 
integrating  watt-hour-meter. 

Other  recording  instruments  may  also  be  employed 
in  special  cases,  such  as  recording  amperemeters  and 
voltmeters,  the  latter  being  especially  useful  as  a 
check  on  the  station  superintendent,  since  it  shows 


GENERATING  STATION  SWITCHGEAR    35 


how  the  pressure  has  been  maintained,  and  how  far  it 
has  been  allowed  to  deviate  from  normal. 

The  Home  Office  rules  in  connexion  with  all  mining 
electrical  installations  insist  that  the  leakage  current 
shall  be  kept  within  specified  limits  and  due  provision 
must  be  made  for  measuring  the  actual  leakage 
current,  which  must  not,  under  any  circumstances, 
exceed  one-thousandth  of  the  maximum  supply 
current ;  further  means  must  be  provided  for  immedi- 
ately localizing  any  undue  leakage. 

Several  types  of  leakage  indicators  have  been 
designed  to  fulfil  the  required  conditions,  and  the 
following  particulars  regarding  one  or  two  of  the 
best-known  types  will  show  the  general  principles 
involved. 

A  leakage  indicator  by  Messrs.  Nalder  Bros.  & 
Thompson,  for  use  in  connexion  with  continuous- 
current  circuits,  having  both  mains  insulated,  is 
shown  in  Fig.  9.  With  this  device  a  high  resistance, 
of  not  less  than  200, 000  ohms,  is  connected  across  the 
mains,  and  the  instrument,  of  moving  coil  type,  is 


Ground 


Detector 


FIG.  9.     CONTINUOUS -CuBBENT   LEAKAGE   INDICATOB. 

connected  between  the  mid  point  of  this  resistance, 
through  the  switch,  to  earth,  as  shown  in  the  diagram. 
With  the  switch  in  its  normal  position  the  instrument 
acts  as  an  indicator  of  the  condition  of  the  mains  ; 


36  ELECTRICAL  MINING  INSTALLATIONS 

if  the  pointer  rests  in  the  centre  of  the  scale  it  indi- 
cates equality  in  the  insulation  resistance  of  the  mains  ; 
a  deflection  to  right,  or  left,  indicates  faulty  insulation 
of  the  negative  or  positive  main  respectively. 

A  2-way  switch  is  also  supplied,  and,  in  order  to 
determine  the  exact  value  of  the  insulation  resistance, 
this  is  turned  to  the  right,  and  then  to  the  left,  the 
deflection  being  noted  in  each  case ;  from  these 
observations  the  insulation  resistance  of  both  mains, 
and  also  the  leakage-current  to  earth  may  be  calculated, 
but  in  order  to  eliminate  the  necessity  for  these 
calculations,  a  table  of  values  is  supplied  with  the 
instrument,  from  which  the  insulation  resistance  of 
both  mains,  and  the  current  to  earth  in  milliamperes, 
can  be  read  off  at  a  glance.  The  switch  can  only  be 
left  in  the  centre  position,  and,  consequently,  there 
is  no  likelihood  of  the  main  being  left  connected  to 
earth  through  a  relatively  low  resistance. 

It  is  quite  easy  to  provide  this  leakage  indicator 
with  an  alarm  arrangement,  so  that  when  the  earth 
current  exceeds  the  limit  allowed  by  the  Home  Office 
rules,  a  bell  is  caused  to  ring  in  the  station,  thereby 
calling  attention  to  the  fact. 

For  alternating  current  work  the  same  makers 
have  designed  a  leakage  indicator  suitable  for  use 
where  the  neutral  point  is  earthed  and  also  on  a  mesh- 
connected  three-phase  system. 

The  principle  made  use  of  in  this  instrument  is  that 
of  super-imposing  a  small  continuous  current  on  the 
alternating  system.  This  continuous  current  is 
measured  by  means  of  a  permanent  magnet  moving 
coil  instrument,  which^is  unaffected  by  alternating 
currents. 

'  A  source  of  direct  current  may  be  either  a  primary 
or  secondary  battery,  small  generator,  or  the  exciter 
of  the  alternating  current  generator,  but,  generally 
speaking,  a  dry  battery  of  about  50  volts  is  recom- 
mended. The  moving  coil  instrument  is  so  cali- 
brated with  the  low- voltage  battery,  or  other  source 


GENERATING  STATION  SWITCHGEAR  37 

of  ^continuous  current,  as  to  indicate  directly,  in 
ohms,  the  insulation  resistance  ^between  the  system 
and  earth. 

In  addition  to  the  scales  of  ohms,  the  dial  of  the 
instrument  has  also  [a  scale  of  amperes  marked  on 
it.  The  actual  leakage  current  is  never  greater  than 
the  number  of  amperes  shown  by  the  instrument, 
although,  under  certain  conditions,  it  may  be  less. 

In  the  event  of  the  insulation  resistance  of  the 
system  falling  below  Home  Office  requirements,  a  fuse 
is  blown  and  closes  a  local  bell  circuit,  thus  calling 
attention  to  the  fault. 

The  diagram,  Pig.  10  (a),  shows  the  general'arrange- 


FIG.  10.     DIAGRAM  FOE,  THREE-PHASE  LEAKAGE  INDICATORS. 


38  ELECTRICAL  MINING  INSTALLATIONS 

ment  for  completely  insulated  three-phase  circuits 
from  which  it  will  be  noted  that  a  large  inductive 
resistance  /  is  inserted  in  series  with  the  ammeter ; 
this  prevents  the  flow  of  any  appreciable  alternating 
current  to  earth  through  the  instrument.  This 
resistance  1  takes  the  form  of  a  choking  coil,  enclosed 
in  an  iron  case,  and  provided  with  specially  insulated 
terminals,  so  as  to  be  suitable  for  connecting  to  a  high 
tension  circuit  if  necessary. 

Fig  10  (b)  shows  the  arrangement  for  circuits  with 
earthed  neutrals,  and  it  will  be  noticed  that  the  instru- 
ment is  inserted  between  the  neutral  connexion  and 
earth,  the  resistance  of  instrument,  fuse,  and  battery 
being  only  about  5  ohms,  or  if  the  exciter  is  employed 
only  about  1  ohm  ;  consequently,  the  earthing  of  the 
neutral  is  in  no  way  impaired.  To  prevent  the 
neutral  wire  being  entirely  disconnected  from  earth 
when  the  fuse  blows,  a  resistance  R  is  connected  in 
parallel  with  it,  just  large  enough  to  prevent  the 
current  through  the  instrument,  due  to  a  leak,  doing 
any  damage. 

The  advantage  of  the  above  apparatus  lies  in  the 
fact  that  the  earth  current  is  never  greater  than  the 
reading  shown  on  the  instrument,  and,  further, 
capacity  currents  do  not  affect  the  indicators  in  any 
way. 

When  a  fault  has  been  indicated  by  the  alarm  bell, 
localization  may  be  carried  out  with  an  ordinary 
insulation  testing  set. 


CHAPTER   IV 
TRANSMISSION 

THE  whole  question  of  the  transmission  of  electrical 
energy  is  most  important,  in  fact,  the  cost  of  trans- 
mission is  often  the  determining  factor,  in  deciding 
upon  the  best  system  for  any  particular  installation. 

It  is  assumed  that  the  general  principles  governing 
the  selection  of  any  particular  system,  are  more  or 
less  understood,  but  the  limitations  may  be  briefly 
stated  as  follows  : — 

Continuous  current,  at  220  volts,  for  lighting  in 
compact  districts. 

Continuous  current  at  400  to  500  volts  for  mixed 
lighting  and  power  work  in  a  more  extended  district, 
the  lighting  being  arranged  on  the  three -wire  system. 

Continuous  current  at  400  to  600  volts  for  motors 
only,  in  an  extended  district,  assuming  that  the 
distances  are  not  excessive. 

Three-phase  supply,  at  400  to  600  volts  would  be 
adopted  under  the  same  conditions  as  the  last  named, 
but  there  may,  of  course,  be  other  circumstances  in 
favour  of  three-phase  supply.  This  matter  is  gone 
into  more  fully  in  Chapter  I. 

Three-phase  supply,  at  2,200  to  3,300  volts,  would 
be  used  where  the  energy  had  to  be  transmitted  a 
considerable  distance,  say  2  to  8  miles. 

Three-phase  supply,  at  5,000  volts,  and  upwards, 
would  be  used  for  long  distance  transmission. 

Any  lighting  that  may  be  required  on  the  three- 


40     ELECTRICAL  MINING  INSTALLATIONS 

phase  system  is  easily  provided  for  by  installing  a 
transformer  to  give  the  required  pressure. 

In  the  case  of  three-phase  supply,  a  periodicity  of 
50  cycles  will  probably  be  chosen  for  a  mixed  lighting 
and  power  load,  but  for  long  distance  transmission, 
with  power  load  only,  a  periodicity  of  25  cycles  will 
have  some  advantages. 

For  short  distance  transmission  insulated  cables 
laid  underground  will  probably  be  used  ;  but  where 
it  is  practicable  to  adopt  overhead  conductors,  the 
cost  will  be  considerably  lower,  especially  for  long 
distances.  The  method  of  calculating  the  size  of 
conductor  required,  will  be  much  the  same,  which- 
ever system  is  used. 

The  size  of  the  conductors  will  depend  upon  : — ~] 

(a)  The  current  to  be  transmitted. 

(b)  The  permissible  voltage  drop. 

(c)  The  permissible  current  density. 

The  current  to  be  transmitted,  is,  of  course,  deter- 
mined by  the  power  required,  the  particular  system 
to  be  adopted,  and  the  voltage. 

The  permissible  voltage  drop  depends  upon  circum- 
stances, but  its  usual  value  is  of  the  order  of  2J  per 
cent,  for  lighting,  and  5  per  cent,  for  power,  except  for 
long  distances,  when  the  drop  may  be  10  per  cent.,  or 
even  15  per  cent,  for  very  long  lines,  of,  say,  20  miles 
or  more.  The  voltage  drop  is  a  function  of  the  current 
transmitted,  the  size  of  conductor,  and  the  distance. 

The  permissible  current  density  is  usually  calcu- 
lated on  the  basis  of  1,000  amperes  per  square  inch  ; 
under  the  more  scientific  reckoning  of  the  Institu- 
tion of  Electrical  Engineers  the  values  vary  for  differ- 
ent size  cables,  as  shown  in  the  accompanying  table. 
This  current  density  only  applies  to  insulated  con- 
ductors and  no  such  limitations  are  imposed  on  bare 
overhead  wires,  of  which  the  size  usually  depends 
upon  the  permissible  voltage  drop. 

Strictly  speaking,  there  is  another  factor  to  be 
considered.  So  far  we  have  only  taken  the  technical 


TRANSMISSION  41 

points  into  account,  but  it  is  evident  that  commercial 
considerations  are  equally  important.  For  instance, 
although  we  may  save  money  by  employing  a  con- 
ductor of  small  size,  the  energy  loss  will  be  relatively 
great,  and  this  costs  money  to  produce,  so  that  we 
may  be  saving  on  prime  cost  and  losing  on  working 
costs. 

In  1881  Kelvin  investigated  with  a  view  to  dis- 
covering under  what  conditions  both-  the  value  of  the 
line  and  that  of  the  energy  lost  in  transmission  were 
respectively  a  minimum.  The  result  is  embodied  in 
the  following  formula,  known  as  "  Kelvin's 
Law." 

"  The  cost,  per  annum,  of  the  line  losses,  must  be 
equal  to  the  annual  interest,  and  the  depreciation  of 
the  line." 

We  can  here  only  briefly  state  the  law,  but  it  has 
been  found,  by  experience,  that  it  is  only  in  connexion 
with  large  and  important  schemes  that  it  is  necessary 
to  apply  it  in  practice. 

To  take  a  general  example  of  the  procedure  in 
determining  the  size  of  conductor  for  continuous 
current  transmission,  assuming  the  power  to  be  trans- 
mitted, the  voltage,  and  the  distance,  to  be  known. 
The  maximum  current  is  first  obtained,  by  dividing 
the  power  in  watts,  required  at  the  far  end  of  the  line, 
by  the  voltage  at  that  end.  In  the  case  of  an  insu- 
lated conductor  this  will  usually  suffice,  by  reason  of 
the  current  density,  but,  after  selecting  the  required 
size  of  cable  from  the  makers'  list,  it  will  be  as  well  to 
again  check  the  size  by  multiplying  the  total  resistance 
(lead  and  return)  by  the  current,  to  ensure  that  the 
pressure  drop  is  not  excessive.  If  the  pressure  drop 
is  too  great,  a  larger  cable  must  be  employed.  It  will 
not,  however,  be  possible  to  adopt  a  smaller  cable  if 
the  pressure  drop  is  found  to  be  small,  for  the  mini- 
mum size  has  already  been  fixed  by  the  permissible 
current  density. 

In  the  case  of  an  overhead  bare  conductor,  the 


42     ELECTRICAL  MINING  INSTALLATIONS 

usual  plan  is  to  first  settle  the  permissible  pressure 
drop,  then,  dividing  this  by  the  current,  we  obtain  the 
total  resistance  of  the  conductor  required.  With  this 
information  the  size  can  now  be  easily  chosen  from 
the  table.  This  conductor  can  in  all  probability  be 
employed  provided  that  the  current  density  is  not 
excessive,  in  which  case  there  will  be  danger  of  the 
wire  overheating.  Current  densities  up  to  3,000 
amperes  per  square  inch  may  be  used  for  bare,  and 
about  2,000  amperes  per  square  inch  for  braided, 
aerial  wires,  and  these  values  will  be  found  to  cover 
nearly  all  cases  in  practice. 

There  is  one  other  point  to  remember  in  connexion 
with  overhead  wires,  viz.,  that  a  No.  8  S.W.G.  is 
the  smallest  permissible  single  conductor  from  a 
mechanical  standpoint. 

For  a  three-phase  transmission  system  we  proceed 
in  a  similar  manner.  If  the  conductor  be  insulated, 
and  its  size  consequently  fixed  by  the  current  density, 
we  first  obtain  the  current  per  phase  by  dividing  the 
apparent  watts  by  the  voltage,  and  the  quotient  by 
\/3  ;  allow  1,000  amperes  per  square  inch,  or,  in  the 
case  of  large  cables,  calculate  the  area  on  the  basis 
established  by  the  Institution  of  Electrical  Engineers. 

It  will  be  noted  that  the  size  of  conductor  is  based 
on  the  apparent  watts  and  not  on  the  true  watts  ; 
i.e.,  due  allowance  must  be  made  for  the  power  factor 
when  determining  the  sizes  of  cables.  The  reason 
will  be  apparent  on  referring  to  the  general 
principles  of  three-phase  working,  in  the  first  chapter. 

It  will  be  necessary  to  check  the  size  thus  obtained, 
to  see  that  the  drop  in  pressure  is  not  excessive.  This 
is  done  by  taking  the  resistance  of  the  particular  con- 
ductor or  cable  from  the  annexed  table,  or  from  the 
makers'  list,  and  multiplying  by  the  current  per  phase. 
The  resistance  must  be  that  of  a  single  line,  and  the 
fall  in  pressure,  given  by  the  formula,  will  then  be  the 
volts  lost  along  that  line.  In  order  to  find  the  drop  in 
volts  between  lines  (this  being  the  usual  way  of  measur- 


TRANSMISSION  43 

ing  three-phase  alternating  pressure)  the  result  must 
be  multiplied  by  V& 

In  the  case  of  an  overhead  three-phase  transmission 
line,  with  bare  conductors,  where  the  size  is  mostly 
settled  by  the  permissible  pressure  drop,  we  proceed 
in  the  same  way  as  for  continuous  current,  not  for- 
getting the  factor  V3.  For  convenience  in  calculation 
the  Author  has  prepared  the  following  formula,  which 
will  give  the  correct  size  of  conductor,  in  a  three-phase 
transmission  scheme  at  once  when  the  distance, 
current,  and  permissible  voltage  drop  are  known, 

T  v  0 

— — = Sectional  area  of  each  conductor  in  square 

J-^  V    /\    ^rfc 

inches. 

Where  L  =  distance  in  thousands  of  yards. 

Where  C  =  current  per  phase. 

Where  LV  =  the  permissible  lost  volts  or  pressure 
drop. 

It  is,  of  course,  probable  that  there  will  not  be  a 
standard  size  of  cable  to  fit  in  exactly  with  the  result, 
and  the  nearest  standard  size  must  be  adopted.  It 
would  be  advisable  to  again  check  the  result,  if  the 
cable  differs  much  from  the  value  required,  and  this  is 
best  done  by  taking  the  actual  resistance  from  the  list 
or  table,  multiplying  by  the  current  per  phase,  and 
by  \/3  when  the  result  should  not  differ  much  from  the 
pressure  drop  allowed  for  in  the  first  formula. 

As  a  large  number  of  British  collieries  are  now  using 
bare  overhead  mains  supported  on  poles  it  will  not  be 
out  of  place  to  give  a  few  general  particulars  of  this 
system,  before  proceeding  to  a  consideration  of  insu- 
lated cables  for  surface  and  underground  use. 

In  the  first  place,  the  wires  or  conductors  should  be 
of  hard-drawn  high  conductivity  copper.  This  is 
necessary  on  account  of  mechanical  strength.  Alu- 
minium conductors  are  employed  in  a  few  instances, 
but  this  metal  has  several  disadvantages  compared 
with  copper,  although,  when  the  market  price  of  copper 


44    ELECTRICAL  MINING  INSTALLATIONS 

is  high,  alluminium  will  show  some  advantage  in 
first  cost. 

It  is  common  practice  to  use  bare  copper  wires,  but, 
in  some  instances,  conductors  covered  with  a  single, 
double,  or  triple  layer  of  braid,  served  with  a  special 
weather-resisting  compound,  are  used.  Such  a  con- 
ductor may  consist  of  a  single  wire  or  be  made  up  into 
a  strand  of  seven,  nineteen,  thirty-seven  wires,  etc., 
acording  to  the  capacity  required.  It  must  be  under- 
stood that  the  braiding,  and  serving  of  compound,  are 
not  relied  upon  for  insulating  purposes,  but  merely  as 
a  protection  against  chemical  fumes  or  the  weather. 

Bare  conductors  are  more  usually  solid,  and  not 
stranded.  The  size  of  any  one  conductor  may  be 
anything  from  No.  8  S.W.G.  up  to  No.  000  S.W.G., 
the  latter  being  as  large  as  is  convenient  to  handle. 
If  a  still  larger  capacity  be  required,  two  or  more 
single  conductors  of  the  requisite  size  may  be  run  in 
parallel  on  the  same  poles. 

If  the  capacity  required  be  considerable,  say  200 
amperes  or  more,  a  stranded  cable  of  the  necessary  area 
may  be  used.  It  is  obviously  impossible  to  support 
such  a  cable  on  poles  the  usual  distance  apart,  and 
in  such  cases,  the  cable  may  be  made  up  of  soft  copper 
strand,  for  convenience  in  handling,  and  slung,  at 
frequent  intervals,  from  a  steel  suspension  wire,  by 
suitable  suspenders,  the  suspension  wire  being  carried 
on  insulators  in  the  usual  way.  The  stranded  wire, 
in  such  case,  is  usually  braided,  and  treated  with 
weather-resisting  compound. 

Poles  for  supporting  overhead  transmission  lines 
are  usually  of  wood,  although  steel  poles  are  sometimes 
used.  The  former  are  mostly  of  redwood,  well 
creosoted,  in  order  to  resist  the  weather.  On  a 
straight  run  they  would  be  spaced  about  130  feet 
apart,  i.e.,  about  40  to  the  mile,  but  on  curves,  and 
through  rough  country,  it  may  be  necessary  to  place 
them  closer  together. 

They  are  generally  from  20  to  40  feet  in  length, 


TRANSMISSION  45 

the  diameter  (usually  measured  5  feet  from  the  butt, 
or  large  end)  being  anything  from  6  to  12  inches  accord- 
ing to  length  of  pole,  and  the  strength  required.  For 
light,  single  lines,  single  poles  may  be  used,  but  for 
heavy  lines,  it  may  be  advisable  to  adopt  A,  or  H 
poles,  in  order  to  secure  the  necessary  strength  with 
a  minimum  of  timber.  Fig.  11  shows  the  single,  A, 
and  H  poles  respectively,  together  with  the  usual 
arrangement  of  cross  arms.  The  illustration  also 
shows  bracing  and  stay  wires.  They  depict  poles  by 
Messrs.  Wade,  and,  in  a  recent  paper  before  the 
Institution  of  Electrical  Engineers,  Mr.  C.  Wade  gave 
the  results  of  experiments,  carried  out  to  determine  the 
relative  strengths  of  various  sizes  and  forms  of 
pole. 

Space  will  not  permit  full  particulars  here,  but  it 
may  be  stated,  briefly,  that  the  A  pole  appears  to  be 
most  satisfactory  for  heavy  lines,  where  a  single  pole 
cannot  be  used,  and  is  about  four  and  a  half  times  as 
strong  as  a  single  pole  of  equal  area,  in  a  direction  of 
right  angles  to  the  wires,  and  about  twice  as  strong  in 
the  direction  of  the  wires.  The  spread  of  the  pole 
should  be  about  |-  of  the  height. 

The  H  pole  is  chiefly  used  as  a  terminal  pole  at  the 
end  of  a  transmission  line.  For  this  position  the 
double  H  pole  is  often  used  as  suitable  for  taking  the 
heaviest  strains. 

The  cross  arms  may  be  of  oak,  or,  if  preferred,  of 
galvanized  iron.  In  a  continuous-current  system,  an 
insulator  will  probably  be  fixed  at  each  end  of  the 
cross  arm,  and,  if  more  than  one  pair  of  conductors 
has  to  be  carried,  a  separate  cross  arm  will  be  pro- 
vided for  each  pair. 

For  three-phase  transmission  it  is  usual  to  dispose 
the  wires  in  the  form  of  a  triangle,  one  insulator  being 
fixed  at  each  end  of  the  cross  arm  and  the  other  at  the 
top  of  the  pole.  If  two  three-phase  lines  have  to  be 
carried  they  may  be  arranged  on  three  cross  arms,  one 
complete  three-phase  circuit  on  either  side  of  the  pole, 


46  ELECTRICAL  MINING  INSTALLATIONS 


TRANSMISSION  47 

the  conductors  being  one  above  the  other,  or,  alter- 
natively, as  shown  on  the  A  pole  in  Fig.  11. 

Lightning  arresters  are  installed  at  both  ends  of 
the  line  and  also  at  every  point  where  power  may  be 
taken  from  it  en  route.  Such  lightning  arresters  may 
conveniently  be  placed  in  the  station,  or  substation, 
together  with  the  necessary  choking  coils.  These 
latter  are  necessary  to  ensure  that,  in  the  event  of  the 
line  being  struck,  the  discharge  shall  not  reach  the 
generators  and  motors,  otherwise  the  insulation  would 
most  certainly  suffer. 

On  long  lines  it  is  also  customary  to  place  lightning 
arresters  at  equi-distant  points  along  the  route,  usually 
every  half-mile  ;  these,  however,  are  merely  earthed, 
and  choking  coils  are  unnecessary.  In  some  cases  a 
galvanized  iron  wire  is  run  up  each  pole  to  form  a 
lightning  conductor.  This  wire  projects  some  few 
inches  beyond  the  top  of  the  pole,  while  at  the  base 
an  earth  is  obtained  by  coiling  a  length  of  the  wire  in 
the  form  of  a  spiral  and  burying  it  in  the  ground.  It 
is  possible  that  this  form  of  lightning  protector  may  be 
efficacious,  and  it  has  the  advantage  of  being  cheap, 
but  is  no  good  unless  the  earth  connexion  is  properly 
made.  In  all  cases  where  a  reliable  earth  connexion 
is  necessary,  copper  earth  plates  should  be  used. 
These  should  be  about  4  feet  square,  and  should  have 
a  substantial  lug  riveted  or  brazed  on,  for  connecting 
purposes. 

Such  an  earth  plate  is  then  buried  deep  below  ground, 
in  a  bed  of  coke.  Provided  the  ground  is  moist,  this 
will  make  an  efficient  and  reliable  earth  connexion, 
but  in  some  positions  owing  to  the  nature  of  the  ground 
it  may  be  found  necessary  to  keep  the  earth  moist 
artificially  by  means  of  a  special  water  supply. 

One  of  the  chief  points  in  connexion  with  an  over- 
head transmission  line  is  the  design  of  the  terminal 
poles  and  leading-in  arrangements.  Where  the  trans- 
mission line  leaves  the  power  station,  or  substation, 
the  connexions  from  the  switchboard  will  probably 


48  ELECTRICAL  MINING  INSTALLATIONS 

take  the  form  of  a  three-core  armoured  cable,  which 
may  be  laid  underground,  to  the  base  of  the  terminal 
pole,  then  cleated  up  the  pole,  and  led  into  a  special 
form  of  branching  box,  from  which  the  separate  leads, 


FIG.   12.     TERMINAL  POLE. 


to  the  three  transmission  wires,  (assuming   a  three 
phase  supply)  would  be  taken. 

With  such  an  arrangement  the  lightning  arresters 


TRANSMISSION  49 

will  have  to  be  placed  in  the  station.  If,  however,  it 
is  desired  to  fix  the  lightning  arresters  on  the  terminal 
pole,  the  arrangement  will  be  as  shown  in  Fig.  12. 
Several  alternative  designs  are  possible,  but  the  one 
shown  is  typical.  It  will  be  seen  that  the  incoming  or 
outgoing  transmission  line  is  terminated  on  some  form 
of  shackle  insulator,  provision  being  made  to  take  the 
strain  off  the  last  span.  The  connexion  is  then  formed, 
by  another  bare  copper  conductor,  from  the  lightning 
arrester  to  the  insulated  cable  leaving  the  pole.  The 
particular  type  of  arrester  shown,  is  that  known  as  the 
"  Wurtz,"  and  consists  of  a  number  of  serrated  metal 
cylinders,  mounted  close  to  one  another,  but  preserv- 
ing a  sufficient  distance  to  prevent  the  line  pressure 
from  jumping  the  gap.  The  high  tension  lightning 
discharge  easily  crosses  the  intervening  space,  and 
passes  to  earth  by  way  of  the  earth  plate,  the  main 
current  being  prevented  from  following  or  setting  up 
an  arc,  by  virtue  of  the  special  non-arcing  metal,  of 
which  the  cylinders  are  composed.  In  addition  to 
the  metal  cylinders,  there  are  resistances  in  series 
and  in  parallel,  to  secure  the  proper  working  of  the 
apparatus. 

Above  the  lightning  arrester  will  be  noted  the  isolat- 
ing switch,  which  renders  the  apparatus  "  dead  "  for 
purposes  of  inspection  and  adjustment. 

The  connexion  to  the  three-core  cable  is  made 
through  a  few  turns  of  bare  copper  conductor,  which 
form  a  choking  coil,  and  prevent  the  high  tension, 
high  frequency,  lightning  discharge,  from  passing 
along  the  cable.  The  connexion  from  the  choking 
coil  is  led  into  the  cable  box  and  properly  sealed. 
This  box  encloses  the  connexion  between  the  bare 
conductor  and  the  insulated  cable  leading  down  the 
pole  away  to  the  power  station  or  substation  as  the 
case  may  be. 

The  cable  in  this  particular  case,  is  run  inside  a 
steel  pipe,  cleated  to  the  pole  as  shown.  With  such  an 
arrangement  of  terminal  pole,  it  is,  of  course,  abso- 


50  ELECTRICAL  MINING  INSTALLATIONS 

lutely  necessary  to  provide  a  complete  housing  round 
the  lightning  arresters,  isolating  switches,  and  chok- 
ing coils,  to  protect  them  from  the  weather. 

If  the  overhead  transmission  line  is  from  the  power 
station  to  a  pit  shaft,  the  connexion  at  the  latter  end 
should  be  taken  to  a  switch  panel,  on  which  are 
mounted  the  lightning  arresters,  isolating  switches 
and  choking  coils.  This  panel  may  be  placed  in  an 
adjacent  building,  or  set  up  in  a  suitable  cast-iron 
pillar,  erected  at  the  foot  of  the  terminal  pole.  It 
will  be  noted  that  the  switches  shown  only  isolate  the 
lightning  arresters,  and,  if  it  is  required  to  discon- 
nect the  transmission  line  from  the  outgoing,  or  incom- 
ing, cables,  another  set  of  isolating  switches  must  be 
provided  for  the  purpose. 

The  special  rules  covering  the  installation  and  use 
of  electricity  in  mines,  require  that  an  efficiently 
enclosed,  locked  switch  box,  or  switch  house,  shall  be 
provided  near  the  pit  mouth,  for  cutting  off  the  supply 
of  electricity  to  the  mine,  if  the  generating  station  is 
not  within  400  yards  of  the  pit  mouth.  In  practice 
it  will  be  found  convenient  to  provide  this  switch 
in  all  cases  where  an  overhead  transmission  line  is 
used,  especially  as  it  is  such  a  simple  and  inexpensive 
addition. 


52    ELECTRICAL  MINING  INSTALLATIONS 


PARTICULARS 


Amperes  at 

SIZE. 

1,000  per 

DIAMETER. 

AREA. 

square  inch 
at  above 

Amperes 

ratio, 

at 
I.B.E. 

S.W.G. 

Loss  = 
approx.  2£ 
volts  per 

Standard. 

Inches. 

Square 
Inches. 

100  yards. 

22 

0-6158 

1-7 

•028 

•0006158 

21 

0-8042 

2-2 

•032 

•0008042 

20 

1-0179 

2-6 

•036 

•001018 

19 

1-2566 

3-2 

•040 

•001257 

18 

1-8096 

4-2 

•048 

•001810 

17 

2-4630 

5-4 

•056 

•002463 

16 

3-2170 

6-8 

•064 

•003217 

15 

4-0715 

8-2 

•072 

•004072 

14 

5-0265 

9-8 

•080 

•005027 

13 

6-6476 

12-4 

•092 

•006648 

12 

8-4949 

15-0 

•104 

•008495 

11 

10-568 

18-0 

•116 

•01057 

10 

12-868 

21-0 

•128 

•01287 

9 

16-286 

27-0 

•144 

•01629 

8 

20-106 

31-0 

•160 

•02011 

7 

24-328 

36-0 

•176 

•02433 

6 

28-952 

42-0 

•192 

•02895 

5 

35-298 

48-0 

•212 

•03530 

4 

42-273 

57-0 

•232 

•04227 

3 

49-875 

64-0 

•252 

•04988 

2 

59-828 

75-0 

•276 

•05982 

1 

70-685 

85-0 

•300 

•07069 

1/0 

82-447 

97-0 

•324 

•08245 

2/0 

95-114 

108-0 

•348 

•09511 

3/0 

108-68 

120-0 

•372 

•1087 

4/0 

125-66 

135-0 

•400 

•1257 

5/0 

146-57 

155-0 

•432 

•1466 

6/0 

169-09 

173-0 

•464 

•1691 

7/0 

196-34 

196-0 

•500 

•1963 

TRANSMISSION 


63 


OF   CONDUCTORS. 


STANDARD  RESISTANCE  AT 
60°  Fahr. 

STANDARD  WEIGHT. 

SIZE. 

Ohms  per 
1,000  Yards. 

Ohms 
per  Mile. 

Pounds  per 
1,000  Yards. 

Pounds 
per  Mile. 

S.W.G. 

39-05 

68-72 

7-120 

12-53 

22 

29-90 

52-62 

9-301 

16-37 

21 

23-62 

41-57 

11-77 

20-72 

20 

19-13 

33-67 

14-53 

25-58 

19 

13-28 

23-38 

20-93 

36-83 

18 

9-762 

17-18 

28-48 

50-12 

17 

7-478 

13-16 

37-20 

65-47 

16 

5-904 

10-39 

47-09 

,    82-87 

15 

4-784 

8-419 

58-13 

102-3 

14 

3-617 

6-366 

76-88 

135-3 

13 

2-831 

4-982 

98-24 

172-9 

12 

2-275 

4-004 

122-2 

215-1 

11 

1-868 

3-228 

148-8 

261-9 

10 

1-476 

2-598 

188-4 

331-5 

9 

1-195 

2-104 

232-5 

409-2 

8 

•9881 

1-739 

281-3 

495-1 

7 

•8307 

1-462 

334-7 

589-1 

6 

•6813 

1-199 

408-2 

718-4 

5 

•5688 

1-001 

488-8 

860-2 

4 

•4821 

•8484 

576-7 

1015-0 

3 

•4019 

•7073 

692-0 

1218-0 

2 

•3402 

•5987 

817-6 

1439-0 

1 

•2917 

•5133 

953-4 

1678-0 

1/0 

•2528 

•4450 

1099-0 

1935-0 

2/0 

•2212 

•3893 

1257-0 

2212-0 

3/0 

•1913 

•3367 

1453-0 

2558-0 

4/0 

•1640 

•2887 

1695-0 

2983-0 

5/0 

•1422 

•2503 

1955-0 

3441-0 

6/0 

•1225 

•2156 

2270-0 

3995-0 

7/0 

54    ELECTRICAL  MINING  INSTALLATIONS 


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o  o 

00  ^ 
CO  CO 
(M  00 
^*  ^ 
O  O 
00 

O  O 
tO  O5 

CO  CO 

to  oo 
to  to 
o  o 
o  o 

•0070050 
•0086490 

•012460.0 
•0169500 

O  O 
O  O 

T*<    O 
rH   O 

(M  to 

gg 

•0280300 

i 

PH   CO 

lO  CO 

t-  co 

CO  IO 

rt<  co 
to  to 

0  0 

CO  O5 

CO   -H 

§s 

05  CO 

gg 
co  co 

O  O 

(N   rH 

i-H   TJH 

o 

<N 
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^* 

to  co 

00  05 

O   •-! 

1—  1  1—  1 

<M  to 

O  CO 
(N  (M 

CO  CO 
CO  CO 

0 
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i 

CO    T* 

CO  i—i 

00  T* 
CO  CO 
(M  00 

to  CO 
CO  OO 

to  oo 

tO  O5 
g'* 
CO 

O  O 

co  to 

Tt<  05 

o  o 

T*    O 
rH   O 

1 

en 

(M  CO 

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to  to 

t^oo 

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i-H   rH 

C<1  to 
(M  G<l 

00 
(N 

| 

II 

00  O 
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(M  CO 

§§ 

CO  O 

oS 

00  CO 

^  to 

0  0 

^  00 

CO  CO 

o  o 

(M 
t^ 

0 

to 

(M 

T*    CO 

<N  <M 

HN 

(M  S 

HN 

•-H    O 

(M  (M 

O  05 

<N   r-l 

00  l> 

—   rH 

co 

rH 

to 

rH 

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l>t> 

t*t>- 

t^t> 

l>t>« 

l>t^ 

l>  t^ 

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56      ELECTRICAL  MINING  INSTALLATIONS 


-«j 

OS  IO 

00  C^ 

10  10     ;     o  o 

O  rH                  -HH   CO 

g*s| 

IIS 

OS  ?M 

cp  10 

OS   rH 

CO  C^               O  CO 

SM 

a  - 

O  05 
CO  ^ 

<N  00 
1^  CO 

t-  00 

CO  (N 

CO  (M 

00  !>• 

OO  (N 

OO02 

PH  c«fi 

(M  OS 

00  t^ 

0  ^H 

CO  OO 

a 

03 

rH 

CO  (M 

O  CO 

o  co 

0^ 

00  0 

isi 

*S 

^5  10 

Tt<  os 
oo  os 

IO  CO 

O  OS 
1—  10 

00  O 

t-  O 

CO  00 

PH   i-H 

lil 

5     . 

O  rH 

00 

00 

IO  CO 

d^o 

£  3,2                    oiOO  CO 
n    "^                        rS  G^l  CO 

CM  CO 

rH  ^          t         O1  CO 

^  jSS                   ""t^  OS 

O  (M 

IO  00        i       (M  CO 

CQ 

pH  PH 

PH  PH 

—  :  —       — 

£* 

OS  IO 

§10 

S  10 

00  O 

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11 

CO   Tt< 

9  9 

00 
10 

9  9 

99 

PH    IO 

99 

CAPACITY. 

l5l 

o  o 

GO  rH 

CO  CO 
CO  l> 

o  o 

os  co 

l>  CO 

00  O 
pH 

co  os 

CO  p 
OS  ^ 

g 

& 

A 

-^  0<  II  ^B, 

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OS  IO 

IO  t^» 

O  10 

Ol  10 
l>  IO 

00  O 

m 

T»<   10 

O  CO 

(M  OO 

PH   10 

% 

CO   T^ 

10  10 

pH   PH 

o 

351  PS 

**  Q 

°§ 

1 

O  (M 

oo  os 

0  0 

10  Tj< 

OS  O 

O   rH 

CO  OO 
PH   (M 
PH   PH 

00  (M 

il 

M 

Bfi 

3  w 

•2  • 

2  o 

sg 

II! 

PH   PH 

1    rH 

rH  O 
pH  PH 

8S 

CO 

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os  os 

PH  PH 

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j 

i 

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TRANSMISSION 


57 


COO 
CD  O 
CO  CO 
CM  O 

IO  T* 

CO  CO 

-H  CO 

t-  »0 

o  t-~ 

CO  O 
CO  O 

^    Tj< 

t^lO 

CO  CD 
r-H  IO 
CO  (M 

0§ 

T*  05 

O  CO 

CD  10 
rH   rH 

rH  rH 

CO  CO 
O  f- 

10  CO 
CO  10 

i-H  i-l 

(M 

§0 
CD 
CO  O 
CM  00 

Q"4 

*H<    rH 

10  GO 
CO  O5 

g 

CO  O 

co  r- 

•^  CO 
l>-  i—  i 

10  1O 

10  ^ 

TH  1O 
05  rH 
CO  ^ 
T*   CO 

^*  rH 
CO  t^ 
CO  CO 
CO  CO 

SS 

rH  t" 
CO  rH 

§05 
t- 
^  (M 
rH  05 

CO  rH 

1—1 

10 

CO 

r~i 

00 

00 

00 

o  o 

00 

00 

00 

05  O 

CO  rH 

CO  CO 
COCO 

10   rH 

O  0 

^  10 

r-t   O 

05  GO 
10  t- 

r-i  1O 
••H  GO 
O5  i-H 
l-H 

CO  CO 

co  co 

rH   TjH 
rH  rH 

CO  rH 

05  O 
t^  O5 
rH  i-H 

CO  O 

co  co 

CO  CO 

coco 

CO  CO 

"#  ^ 

ri<  10 

00 

O  O 

O  O 

O  O 

O  O 

o  o 

00 

CO  IO 

rH  10 
O  05 

Tt<  ^ 

CO  O 

1—  1  r- 

l>  O5 

rH  |>. 

T*  CD 
OC<I 

T—  i    1—  1 

I—  1  1—  1 

O  05 

CO  rH 

O  CD 
CO  (M 

CD  CO 

23 

CO  CO 

CO  O5 
CD  CO 

rH   O 

^  IO 

rH   T*< 

GO  CD 
t^«  O5 

O5  CO 
05  T* 

oo  co 

rH  CO 
O  O 

1O  CO 

i—  05 

CO  10 

§s 

§o 
o 
o  o 

1O  CD 
00 

§co 
ir- 

1O  CO 

s§ 

O  O 

o  o 
o  10 

O  CO 

rH   rH 

o  co 

O  CO 

o  co 
10  10 

o  o 

rH  O 

t^»  O 

05  -* 
rH  CO 

^*  O 
O5  CO 
CD  10 
CO  -* 
0  0 

CO  ^ 
CO  !>• 
05  4< 
CO  CO 

10  CO 
CO  CO 

CO  O 
**  0 

CO  CD 
100 
CO  1O 
CD  t^ 

2g 

rH  CO 

05  O 

0  0 
rH  CO 

CO  CO 

rH  CO 

if 

t^  o 

10  CO 

O  O 

CO  O 
05  4< 
05  CO 

l>-  l>- 

^  o 

O  rH 

IO  CD 

O5  CO 
05^ 
CO  CO 
rH  CO 

10  co 

*r  *•? 

CO  10 

co^ 

o§ 

o  o 

1O  CO 

8? 

10  CO 
l>  O5 

0  0 
0  0 
§10 
CO 

rH   rH 

0  0 

o  •* 

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10  IO 
rH  rH 

28 

t^-6 

23 

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05  CO 

CO  10 

CO  ^* 

CD  O 

CO   T* 

00 

CO  CO 

s§ 

CO  T* 

1O  CD 
00 

CO  0 

t^co 

00 

g§ 

O  O 

l-H  ^ 

o  o 

rH  rH 

sgs 

rH  rH 

CD  O 

COT* 

O  O 

O  05 
COrH 

CO  t- 

rH  rH 

I    CD 
1    -i 

10  ^ 

l-H   I—  1 

I    CO 

1    i-H 

CO 

l-H 

rH   0 
rH  rH 

O  O5 

CO  rH 

O5  05 

05  05 

O5  05 

05  O5 

O5  05 

05  05 

05  05 

t^  l>- 

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58      ELECTRICAL  MINING  INSTALLATIONS 


0   Q   <} 

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rH   10 

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ss 

VI  H 
i50 

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sff 

oo 

Tt<  CO 
CO  -* 

CO  CO 
G<l  CO 

co  oo 

CO  t^ 
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CO  d 

10  10 
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rH   rH 

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j2  1^  o 

CO  CO 
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rH  rH 

oq  co 

0  O 

rH   CO 

OS  Tt< 
C<1   CO 

iil 

^^^ 
CO 

oSOO  OS 
^2CO  OO 

1-1  rH  rH 

OS  *O 
CO  CM 

OS   T^ 

10  10 

GO  O 
CO  T* 

CO  O 

o  10 

i-H    i-H 

10  CO 

H  w-        « 
>•  <1  g  O 
H  fc  °  H 
H  §  H  ^ 

IJ 

00  00 
CO  CO 
10  05 
CO  GO 
O  O 

O  O 
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rH   1O 

rH   G<l 

§8 

o  o 

10  O 
OJ  CO 

*• 

l^jl 

rH   O 

OS  C<l 

O  O 

CO  CO 

O  O 
O  O 

0  0 

1 

fi-ji 

O   Tt< 

X  O 

rH 

OS  !>• 

CM  10 

00  05 

10  OJ 
CO  t^ 

o 

& 

CQ 

•+-"1   O<  ||  ^e, 

M 

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111 

00  00 
CO  CO 
10  05 
CO  00 

il 

II 

II 

G<l  CO 

Se 

1 

00  CO 

•HH   IO 

00 

T*    05 

co  r- 

o  o 

O  G<J 

GO  GO 
O  O 

05  O 
O  rH 

DIAMETER 

BACH  STR4 

ill 

rH*5 

ad 

CO  l>- 

CO  1O 

rH  rH 

21 

2  1 

III 

1  -  1^. 

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S  O  g.S^                                CO  CO 

III 

CO  CO         '       CO  CO 

i 

CO  CO 

TRANSMISSION 


59 


O  r- 

00  05 

t-~  co 

O  O 

!>•  CO 
CO  O 

0  CD 
O  O 

10 

r-H 

XO 

0 

O5  t^ 

^  00 
GO  05 

rH    O 

05  10 
O5  O 
t^  CO 

O  O 

CO  CO 

CO  O 

10  10 

O  O 

CO  O5 
t^  CO 

"*  -^ 
o  o 

CO  O 
CO  00 

T*   CO 

o  o 

CO  !>• 

00  §3 

1—  I  I—  1 

ss 

rH  0 

—   rH 

CO 

i 

.  O 

O5  t^ 
05  CO 
rH   l> 
GO   rH 

!>•  lO 

O  CO 

Tt<    O 
rH   rH 

00  CO 
CO  00 

99 

CO  CO 
CO  t- 
00  t- 

9  9 

T*  O5 
^  CO 

99 

1O  1O 
O  ^* 
I—  i—  I 

CO  •«* 

CO  C— 

^   T* 

CO 

CO 

Mb 

T*   00 

S§ 

CO  GO 

*°£ 

rH  OO 

co  t^ 

CO  ^ 

10  CO 
CO  CO 

TjH    t- 

10  1O 

11 

CO  CO 

CO  O 
CO  O 

co  i> 

rH  1O 

CO  05 
10  CO 
CO  t^ 

i-4  1O 
rH  05 
r-l  CO 
00  00 

00 

t^ 

00 

O5 

rH  CO 

r-io 

O  —  i 

^  10 

CO  TH 

CO   rH 
CO  TjH 
CO  00 

00  O 

^    T* 
10   rH 

O5  O 

S8 

Jt-  CO 

O  rH 

o  10 

CO  I>- 

O  CO 
CO  CO 
rH  rH 

CO  O 

CO  O 
00  O 
O  1O 
CO  CO 

g§ 

CO  O 
00  O 

CO   Tfl 

§ 

t^ 

CO 

T* 

U5  1^ 

-"*  »O 
CO  CO 

rH  CO 

O  O 

l>-  O 

O  O 
O  O 
CO  nn 

O  O 

Tj<    10 

o  o 

CO  O 

o  10 

10  10 

o  o 

O  CO 

fco 
CO 

O  O 

T*    1O 

O  O 

05  O 

O 
(M 

O  O 
^  O 

O  O 

CO  CO 

O  O 
0  0 

2§ 

s§ 

t-~  CO 

oo  —  i 

CO  CO 

CO  O 

T*    10 

CO  CO 

^ 

§ 

»0  l> 

05  CO 
rH   CO 

oo  10 

CO  CO 

o  10 

S3 

CO  00 
CO  1O 

>*   Tj< 

CO  00 

t-  rH 

Tj<    10 

CO  O 
CO  O 

s§ 

§ 

1O  !>• 

•«*  10 

O  O 
!>•  O 

8§ 

0  0 
CO  O 

o  o 

O  CO 

§§ 

CO  CO 

CO  O 
00  O 

CO   T* 

5 

^* 

CO  CO 

O5  TjH 
rH  CO 

O  O 
O  O 
CO  r^ 

s§ 

Th  1O 

00  O 

o  10 

1O  10 

§8 

CO  CO 

^  0 

O   rH 
I—  1   i-H 

CO  00 
i—  1  rH 

S 

r—  1 

T*   CO 
CO  t- 

99 

O  CO 

OO  O5 
00 

00  rH 

^*  00 

o  o 

rH  rH 

O  CO 

rH   rH 
rH   rH 

CO     1 

1-1    1 

rH 

l-H 

O 
i—  1 

CO  10 
I—  1  rH 

T*    CO 

rH  rH 

1 

2  1 

IS 

CO  CO 

CO  CO 

CO 

CO  CO 

CO  CO 

coco 

CO  CO 

co  co 

60      ELECTRICAL  MINING  INSTALLATIONS 


w 

1 

3- 

•-8  -3 

CO  <M 

CO  rH 

O  »O 

CO  rH  OS 

co|0 

CO  rH 

giw 

^2$ 

CO  CO 
0  0 

T*  CO 

O  O 

oo 

gg 

§9  a 

O2  H 

ill 

i>  os 

co  10 

0  0 

CO  GO 

!>•  CO 

O  O 

rH  CO  GO 
OS  1O  rH 

10  10  10 

o  o  o 

GO  OS 

OS  T* 

CO    T* 

CO  (M 

a 

02 

§*« 

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=  00  oq 

10   T^ 

CO  OS 

rH   O 

i>  co 

r^io  co 

OS  rH  CO 
1O  rH   GO 

CO  OS  OS 

1-2 

O  O 
CO  O 
f-  O 

ll§ 

62g 
13  w 

*2 

.2S 

03  TT  OS 

4300  G<J 

CO  O 
1O  "*f 

10  c<j 

000 
CO  TH  O 

rH   O  CO 

0  0 
1O  CO 

os  os 

o  o 

10  (M 

CO  rH 

rr> 

co  co 

oq  T^I 

10  CO  t- 

r-  os 

O  rH 

rH  rH 

(M  (M 

FFBCTIVB 
ECTIONAL 
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>NDUCTOR. 

II 

o  t- 

O  OS 

10  co 

CO  l>- 

o  o 

0  0 

§o 
t- 

O  O  O 

go  o 
O  10 
!>•  GO  GO 

O  OS 
O  (M 

O   TH 

os  os 

O  O 
0  0 

o  o 
o  o 

CQ       Q 

rH  rH 

| 

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t-  O 

0  0 

000 

O  CO 

O  O 

I 

III 

os  os 

(M  O 

1O  CO 

GO  TH 
^*  10 

O  GO  CO 
!>•  OS  CO 

1O  1O  CO 

10  os 

10   rH 
CO  t- 

lO  OO 

g 

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§ 

m  £  w  <*J  £  -3 

0  t- 

0  0 

O  O  O 

O  OS 

0  0 

8 

fiiPi 

O  OS 
10  CO 
CO  I- 

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co  t- 

10  O  10 
t-GO  CO 

OS  OS 

§o 
§ 

rH  rH 

*e 

1 

CO  CO 
rH  rH 

(M  CO 

os  os 
o  o 

rH  T*  CO 
O  O  O 
rH  rH  rH 

O  CO 

rH   rH 
rH  rH 

23 

li 

N 

i1 

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rH 

21 

2  I 

IS 

! 

g 

«     8 

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rH  rH 

CO  CO 

rH  rH 

rH  i—  1  rH 
OS  OS  OS 

rH  rH 

OS  OS 

rH  !>• 

fc 

2  s 

TRANSMISSION  61 

The  tables  given  on  the  foregoing  pages  are  based 
on  the  following  resolutions  adopted  by  the  Engin- 
eering Standards  Committee  : — 

That  a  wire  one  metre  long,  weighing  one  gramme 
and  having  a  resistance  of  0-1508  standard  ohms  at 
60°  F.  (15-6°  C.),  be  taken  as  the  Engineering  Stand- 
ards Committee  (E.  S.  C.)  standard  for  annealed  high 
conductivity  commercial  copper. 

That  copper  be  taken  as  weighing  555  Ibs.  per  cubic 
foot  (8-89  grammes  per  cubic  centimetre)  at  60°  F. 
(15 '6°  C.)  which  gives  a  specific  gravity  of  8«89. 
;  That  the  average  temperature  co-efficient  of  0*00238 
per  degree  F.  (0*00428  per  degree  C.)  be  adopted  for 
commercial  purposes. 

That  2  per  cent,  variation  from  the  adopted  stand- 
ard of  resistance  be  allowed  in  all  conductors. 

That  2  per  cent,  variation  from  the  adopted  stand- 
ard of  weight  be  allowed  in  all  conductors. 

That  an  allowance  of  1  per  cent,  increased  resist- 
ance, as  calculated  from  the  diameter,  be  allowed  on 
all  tinned  copper  conductors  between  diameters, 
0-104"  and  -028"  (Nos.  12  and  22,  S.W.G.)  inclusive. 


CHAPTER    V 
UNDERGROUND  CABLES  AND  FITTINGS 

WE  now  come  to  one  of  the  most  important  sections 
of  this  treatise,  namely,  the  consideration  of  under- 
ground wiring  systems.  There  are  three  distinct 
classes  of  cables  to  be  considered  : — (a)  Shaft  cables, 
(b)  Roadway,  or  inbye  cables  and  (c)  Flexible  or 
trailing  cables. 

The  shaft  cables  require  to  be  well  armoured  and 
insulated  with  non-hygroscopic  materials  (or  should 
hygroscopic  materials  be  used  special  precautions  must 
be  taken  to  prevent  access  of  moisture).  For  under- 
ground distribution  of  power  from  the  shaft  into  the 
workings,  armoured  cables  are  not,  in  many  cases, 
absolutely  necessary,  but  the  insulation  must  still  be 
non-hygroscopic  and  capable  of  resisting  mechanical 
damage.  For  the  flexible  or  trailing  cables,  em- 
ployed in  connecting  such  portable  machinery  as  coal 
cutters,  rock  drills,  etc.,  with  the  distributing  mains, 
twin  or  three-core  cables  are  recommended  (accord- 
ing to  whether  the  system  is  continuous  current  or 
three-phase)  and  these  cables  are  usually  rubber 
insulated  and  finished,  overall,  with  a  flexible  pro- 
tective covering. 

In  considering  the  class  of  cable  to  be  used  for  under- 
ground colliery  work,  it  will  be  evident  that  the  con- 
ditions differ  largely  from,  say,  those  of  a  town  light- 
ing system,  and  it  is  only  a  thorough  appreciation  of 
the  special  difficulties  met  with  in  this  class  of  work 


UNDERGROUND  CABLES  AND  FITTINGS    63 

that  has  enabled  the  various  makers  to  evolve  a 
suitable  class  of  cable. 

The  chief  trouble  experienced  is  perhaps  tnat  due 
to  the  presence  of  water,  which  in  some  cases  may  be 
acid,  or  contain  chemical  salts  in  sufficient  quantities 
to  seriously  damage  the  cables  unless  suitable  pro- 
tection be  afforded.  Another  trouble  is  the  liability 
to  mechanical  damage,  either  through  such  accidents 
as  trucks  fouling  the  cables,  or  a  roof  falling,  and 
bringing  them  down  with  it. 

Dealing  first  with  the  insulating  medium,  we  find 
that  rubber  will  give  us  practically  all  we  require  ; 
but  rubber-covered  cables,  of  large  size,  are  expen- 
sive, and  may  cost  double  the  price  of  similar  cables 
insulated  with  paper,  bitumen,  etc.  Paper-insulated 
lead-covered  cables  have  been  used  for  many  years 
in  connexion  with  town  lighting  schemes,  but  as  this 
class  of  insulation  is  very  hygroscopic,  trouble  has 
occurred  due  to  moisture  penetrating,  and  breaking 
down  the  insulation.  To  guard  against  this,  impreg- 
nated paper  has  been  employed  with  considerable 
success,  but  it  is  still  necessary  to  take  great  care  that 
moisture  does  not  enter,  and  for  this  purpose,  cable 
boxes  must  always  be  used  at  the  end  of  a  line  for 
making  connexions. 

The  insulation  most  favoured  for  colliery  cables  is 
that  known  as  vulcanized  bitumen.  This  substance  is 
non-hygroscopic,  and  also  possesses  the  necessary 
insulating  qualities.  Being  quite  moisture-proof, 
the  lead  covering,  used  with  paper  insulated  cables,  is 
not  required.  Some  of  the  earlier  bitumen  cables 
gave  trouble,  due  to  decentralization  of  the  conductor 
when  the  bitumen  is  softened  by  heat,  as  may  occur 
when  a  cable  is  subjected  to  a  heavy  overload.  For 
this  reason  some  makers  now  supply  cables  with  a 
paper  separator  between  the  conductor  and  the  bitu- 
men. 

We  will  now  consider,  briefly,  the  type  and  class  of 
cable  to  use  for  any  particular  position  or  system  of 


64  ELECTRICAL  MINING  INSTALLATIONS 

supply.  First  "we  will  take  the  case  of  shaft  cables. 
These  can  be  made  up  in  the  form  of  single,  twin,  or 
concentric  cables  for  continuous  current  working, 
whilst  for  three-phase  we  may  employ  three  single 
cables,  or,  alternatively,  a  three-core  cable. 

For  continuous  current,  single  cables  are  preferred. 
The  conductor  may  consist  of  a  strand  of  high  conduc- 
tivity copper  wires,  which  should  be  tinned  if  vulcan- 
ized bitumen  is  used  as  insulation,  otherwise  the 
sulphur  in  the  bitumen  may  attack  the  copper. 
Some  makers  provide  a  strand  filling  substance,  a 
waterproof  compound,  which  renders  it  practically 
impossible  for  water  to  travel  along  the  interstices  of 
the  strand.  The  stranded  conductors  are  sheathed 
with  a  solid  tube  of  bitumen,  under  high  pressure,  then 
taped  with  two  or  more  coats  of  stout  tape,  lapped  on 
spirally  in  reverse  directions,  and  thoroughly  im- 
pregnated with  a  bituminous  preservative  compound, 
and  afterwards  braided  or  armoured  as  the  case  may 
require.  A  three-core  cable  would  be  prepared  in  the 
same  way  ;  but,  after  taping,  the  three  cores  are  laid 
up  together,  the  spaces  being  filled  in  with  jute  fibre 
(or  with  bitumen)  ;  the  whole  is  then  further  sheathed 
with  bitumen,  taped  with  two  or  more  bitumen  tapes, 
and  afterwards  braided  and  compounded,  or  armoured, 
according  to  the  conditions  under  which  it  is  to  be 
used. 

As  already  stated,  for  conductors  down  the  shaft 
two  single  cables  are  preferred  for  continuous  current 
working.  This  method  might  also  be  employed  with 
advantage  for  three-phase  working,  especially  when 
the  sectional  area  of  the  conductor  is  large.  It  will 
be  seen  that  a  three-core  cable  is  naturally  of  consider- 
able diameter,  as  compared  with  single  cables,  and 
an  armoured  shaft  cable  to  transmit  400  amperes 
may  be  as  much  as  3 J  inches  diameter  overall.  These 
large  cables  are  difficult  to  handle,  and,  what  is  per- 
haps more  important,  it  is  impossible  to  manufacture 
them  in  unbroken  lengths  for  very  deep  pits. 


UNDERGROUND  CABLES  AND  FITTINGS    65 

If  single  cables  are  used  for  alternating  current  work 
they  must  not  on  any  account  be  armoured,  otherwise 
there  will  be  an  alternating  magnetic  field  set  up  in 
the  steel  armouring,  which  will  cause  pressure  drop 
and  consequent  loss  of  energy.  For  this  reason,  when 
single  cables  are  used  for  alternating  current  they  are 
merely  braided,  and  treated  with  preservative  com- 
pound. If  it  be  necessary  to  protect  such  cables  in 
the  shaft  against  mechanical  damage,  casing  or 
troughs  must  be  provided  and  this,  of  course,  entails 
expense. 

For  shaft  work  a  three-core  cable  is  generally  used 
for  three-phase  current,  and,  if  owing  to  the  large  area 
required,  and  the  great  depth  of  shaft,  it  is  found 
impossible  to  manufacture  and  handle  in  one  length, 
it  will  be  advantageous  to  split  up  the  cable  into  two, 
or  more,  distinct  three-core  cables  each  of  smaller 
sectional  area,  so  that  the  two  or  three  cables  together 
will  be  used  for  transmitting  the  total  load.  Such  a 
scheme  has  the  additional  advantage  of  allowing  one 
cable  to  be  laid  off  at  a  time  for  test,  or,  in  the  event 
of  anything  going  wrong,  the  most  important  motors 
and  lights  underground  can  be  kept  going  while  one 
of  the  cables  is  being  repaired. 

For  very  wet  shafts  lead  covered  cables  have  been 
employed,  but,  owing  to  the  great  weight  of  the  lead, 
this  method  is  impossible  in  deep  shafts  when  the 
cable  is  hung  or  supported  only  at  infrequent  inter- 
vals. If  trouble  due  to  a  wet  shaft  is  expected,  and 
lead-covered  cable  is  out  of  the  question,  it  will  be 
well  to  employ  a  bitumen  insulated  cable,  strand 
filled,  wormed  and  sheathed  with  solid  bitumen 
instead  of  jute  yarn. 

Shaft  cables,  unless  run  in  casing  or  troughing 
down  the  pit,  should  always  be  double-wire  armoured, 
with  one  exception,  as  a  protection  against  mechanical 
damage.  The  cable,  either  single  (continuous  current) 
or  three-core,  should  be  armoured  with  two  layers  of 
galvanized  steel  wires,  laid  on  in  opposite  directions, 


66  ELECTRICAL  MINING  INSTALLATIONS 

the  whole  being  then  covered,  overall,  with  tarred 
jute  yarn,  and  treated  with  preservative  compound. 
This  outer  covering  is  merely  to  protect  the  galvanized 
steel  wire  armouring  from  corrosion. 

When  cables  are  suspended  vertically  in  the  shaft, 
the  steel  wire  armouring  takes  the  strain,  and  supports 
the  weight  of  the  complete  cable.  The  usual  method 
of  supporting  cables  in  pit  shafts  is  by  means  of  hard 
wood  cleats,  about  4  feet  long,  spaced  from  20  to  40 
yards  apart.  One  of  these  cleats  (by  Messrs.  Callender) 
is  shown  in  Pig.  13,  A,  fixed  to  a  brick-work  shaft  by 
means  of  rag  bolts.  Such  a  cleat  can  be  arranged  to 
carry  one,  two,  or  more  cables  as  required.  Where 
this  method  of  suspension  is  inadmissible,  the  cleats 
may  be  hung  on  chains,  as  shown  in  Fig.  13,  B,  the 
chains  being  attached  to  hook  rag  bolts,  let  into  the 
brickwork,  or  fixed  in  such  manner  as  may  be  most 
convenient. 

Another  method  of  suspending  a  shaft  cable  is 
through  the  medium  of  a  special  form  of  steel  sus- 
pender at  the  top  of  the  shaft,  designed  to  take  the 
whole  weight  of  the  cable.  Such  a  suspender,  by 
Messrs.  Siemens  Bros.,  is  shown  in  Fig.  13,  C.  With  this 
arrangement  it  is  absolutely  necessary  to  effectively 
secure  the  steel  wire  armouring  at  the  point  of  sus- 
pension, for  this  must  carry  all  the  weight.  The 
method  can  be  used,  without  any  further  support  for 
shafts  up  to  400  feet  in  depth  ;  for  deeper  shafts  it  will 
be  necessary  to  add  suspension  cleats. 

There  is  one  other  type  of  shaft  cable  that  must 
be  mentioned  before  leaving  this  part  of  the  subject : 
namely,  "  Manilla  cord  armoured "  cable.  These 
are  usually  of  the  vulcanized  bitumen  type,  but, 
instead  of  steel  wire  armour,  we  have  a  double  layer 
of  hard  manilla  cords,  wound  in  reverse  directions. 
This  covering  is  waterproof,  and  has  the  advantage 
of  being  much  lighter  than  steel-armoured  cables  ; 
but  the  most  important  point  is  that  separate  single- 
core  cables,  of  large  carrying  capacity,  can  be  made 


fcSSSSSsSSSSsssp^^ 


FIG.  13.     SHAFT  CABLE  SUSPENDERS. 

67 


68  ELECTKICAL  MINING  INSTALLATIONS 

in  unbroken  lengths,  and  used  for  three-phase  working 
without  the  loss  of  pressure  and  energy  which  would 
occur  if  steel  wire  armoured  cables  were  used  under 
similar  conditions. 

The  lower  end  of  the  shaft  cable  usually  terminates 
in  a  switch  box  and  distribution  board,  from  which 
smaller  cables  are  run  for  distributing  electrical 
energy  to  the  various  motors  used  underground. 

These  cables  in  the  underground  roads  are  made 
up  and  insulated  like  the  mains  haft  cables  described 
above  ;  but  if  steel  wire  armouring  be  employed, 
one  layer  only  is  sufficient  in  most  cases.  If  the 
cable  is  in  a  position  where  frequent  falls  of  the 
roof  are  experienced,  double  wire  armouring  may 
be  employed,  or,  in  special  cases,  we  may  have  what 
is  known  as  lock-coil  armouring,  which  consists  of 
steel  wires  of  special  section  so  arranged  as  to  fit  into 
one  another  and  form  practically  a  solid  sheath  of 
steel.  This  form  of  armour  is  somewhat  expensive, 
and  would  only  be  used  when  great  mechanical 
strength  is  necessary ;  it  is  the  strongest  armour 
yet  devised  for  cable  protection.  Many  colliery 
engineers  prefer  unarmoured  cables  for  distribution 
in  the  roads,  and  there  is  something  to  be  said  for 
this  arrangement  in  the  case  of  small  installations, 
when  maintenance  is  in  more  or  less  unskilled  hands. 
There  are  several  methods  of  fixing  underground  road 
cables,  and  the  illustration  (Pig.  14)  prepared  by  the 
St.  Helens  Cable  Company  shows  four  methods  at 
present  in  vogue. 

The  first  consists  of  single  unarmoured  cables, 
taped,  jute  yarned,  and  braided,  laid,  either  on  a 
shelf  cut  in  the  wall,  or  in  a  trough  behind  the  props  ; 
the  trough  should,  if  possible,  be  filled  with  bitumen. 
This  method  is  rather  expensive,  but  very  safe,  as 
there  is  no  risk  of  personal  contact. 

The  second  consists  of  unarmoured  single  cables, 
suspended  with  tarred  twine,  behind  the  props,  or, 
where  the  roof  is  good,  laid  on  a  shelf  cut  in  the  side. 


UNDERGROUND  CABLES  AND  FITTINGS  69 

The  third  consists  of  armoured  cables,  single  for 
continuous,    twin    for    alternating,    and   three   core 


Third  Method 


Second 
Method 


Fourth  Method 

FIG.   14.     METHOD  or  RUNNING  CABLES  IN  ROADS. 

for  three  phase,  suspended  either  from  the  props 
(in  front)  or  from  the  roof  timbers. 


70      ELECTRICAL  MINING  INSTALLATIONS 

The  fourth  consists  of  armoured  cables  laid  direct 
in  the  floor,  or  unarmoured  cables  laid  in  troughing 
in  the  floor.  This  is  a  most  excellent  method,  but 
very  expensive,  and  upsets  the  working  of  the  road ; 
provision  must  also  be  made  for  a  rising  floor  by 
leaving  slack  in  brick  chambers  near  the  joint  boxes. 

Where  armoured  cables  are  used  in  a  road  it  is 
absolutely  essential  that  the  armouring  should  be 
continuous,  and  remain  so,  all  branches  and  repairs 
being  bridged  over  in  a  substantial  manner  with 
copper  or  iron  strand,  firmly  clamped  to  the  armouring. 
No  mere  twisting  of  one  wire  round  the  armour 
to  be  allowed.  Further,  the  armour  should  be 
substantially  earthed,  every  hundred  yards,  to  water 
pipes.  If  there  are  no  water  pipes  in  that  particular 
road,  an  old  steel  rope  should  be  laid  in  the  floor 
to  take  its  place,  the  rope  being  connected  to  water 
pipes  at  the  nearest  point.  All  machines,  motors, 
winding  gears,  etc.,  should  be  earthed  in  the  same 
manner.  This  frequent  earthing  is  necessary,  as 
the  bridging  of  the  armour  at  repairs  and  joints  may 
become  defective  in  time,  and  damage  in  that  length 
would  render  the  armour  alive. 

Armouring  is  undoubtedly  useful  in  saving  the 
insulation  from  small  damage,  but  under  a  severe 
blow,  piercing  the  insulation,  a  flash  results  before 
the  fuses  have  time  to  blow ;  with  unarmoured 
cable  there  is  no  flash  since  the  leakage  at  the  fault 
is  only  two  or  three  amperes  ;  but  if  this  leak  is 
not  repaired,  smouldering  may  ensue.  After  every 
fall  of  roof,  therefore,  the  cables  should  be  carefully 
examined  and  any  damaged  spots  repaired.  The 
mine  electrician  should  also  test  the  insulation  of 
the  cables  themselves,  all  motors  being  discon- 
nected ;  he  must  not  be  content  with  a  fairly  high 
insulation,  but  must  insist  on  the  same  value  as 
obtained  before  the  fall,  or  find  out  the  reason  for 
the  decrease. 

When  cables  are  suspended  from  the  roof  timbers 


UNDERGROUND  CABLES  AND  FITTINGS    71 

it  is  usual  to  employ  raw  hide,  or  metal  suspenders. 
These  are  easily  fixed,  and  a  length  of  cable  can  be 
suspended  in  a  very  short  time.  When  frequent 
falls  are  experienced,  flexible  suspenders  may  be 
used.  Pig.  15  shows  a  type  of  flexible  suspender, 
known  as  the  Callender-Ward  patent.  With  this 
arrangement  the  cable  is  safely  supported  so  long 
as  the  suspender  has  to  deal  with  its  weight  alone 
but  in  the  event  of  any  undue  pressure  coming  on 


FIG.   15.     FLEXIBLE  CABLE-SUSPENDER. 


the  cable,  the  suspender  allows  it  to  drop,  and  possibly 
escape  such  damage  as  might  occur  if  it  were  rigidly 
held. 

With  a  cable  system  underground  in  a  mine, 
where  we  have  one  or  more  main  and  sundry  smaller 
distributing  cables,  we  shall  require  joint  and  dis- 
connecting boxes  somewhat  similar  to  those  used 
for  town  lighting.  The  conditions  under  which 
these  boxes  are  used  in  mines  present  many  special 
difficulties  which  are  not  met  with  in  ordinary  surface 
installations,  and  consequently  a  special  study  has 
been  made  of  the  subject  of  suitable  and  efficient 
junction  boxes  for  mine  use. 


72  ^ELECTRICAL  MINING  INSTALLATIONS 

Pig.   16  shows  a  standard  straight-through  joint 


LeadBond 


FIG.   16.     SHAFT  CABLE  JUNCTION  Box. 
box  for  jointing  single  cables  in  vertical  pit  shafts 


UNDERGROUND  CABLES  AND  FITTINGS   73 


when  necessary,   and  Pig.    17,  A,  shows  a  similar 
box   for   three-core   cable   in   horizontal   pit   roads. 


Lead  Bond 


Box  filled  with   Compound 
Teak  Spreader 


Wire  Anchoring 


Lead  Bonds- 


IT. 
FIG.  17.     ROAD  CABLE  JUNCTION  BOXES. 

Fig.  17,  B,  is  an  example  of  a  disconnexion  box  for 
three-core  cable  whilst  Fig.   18,  A,  shows  a  three- 


74    ELECTRICAL  MINING  INSTALLATIONS 

way  network  box  with  disconnecting  links.     A  four- 
way   box,   when   necessary,  would   be   designed   on 


Compound  Level 
Fillh      ~ 


Lead  Bond'  °ox  filled  with   Compound 


Wire  Anchorin. 


WoodFerrules 


FIG.   18.     ROAD  CABLE  JUNCTION  BOXES. 
similar  lines.     Another  type  of  box  often  required 


in  connexion  with  three-core  cables  is  shown  in  Pig. 
18,#,  and  is  known  as  the  trifurcating  box  because 
it  divides  up  the  three  cores  of  a  main  cable  into 
three  separately  insulated  conductors.  This  form 
of  box  is  used  at  the  end  of  a  three-core  cable  as  it 
affords  a  neat  and  effective  means  of  bringing  out 
the  conductors  for  connexion  to  the  switchboard. 
These  illustrations  are  all  of  Messrs.  Callender's 
standard  boxes. 

It  will  be  noticed  that  in  all  these  boxes  the  joints 
are  dry,  as  in  many  cases  it  would  be  impossible 
to  solder  the  connexions  in  the  mine.  The  dis- 
connecting boxes  are  also  shown  with  hermetically 
sealed  lids,  and  are  filled  with  compound  to  a  certain 
level,  and  above  this  again,  with  resin  oil,  in  order 
to  prevent  sparking  when  connexion  or  discon- 
nexion of  a  cable  is  effected.  In  some  few  cases 
it  is  impossible  to  use  compound  in  the  boxes  as  it 
may  be  inadmissible  to  heat  it  in  the  pit  or  to  convey 
it  heated  from  the  surface.  In  such  cases  a  special 
high  insulating  grease  can  be  used,  which,  while 
being  sufficiently  soft  to  apply  without  heating,  is 
too  stiff  to  permeate  the  cable  dielectric  if  of  paper 
or  jute,  or  to  be  drawn  up  the  strands  of  the  conduc- 
tors. Oils  are  not  recommended  for  this  reason  and 
are  only  used  on  the  top  of  a  more  solid  sealing  com- 
pound as  a  spark  preventative.  The  boxes  are 
shown  with  armour  clamps  for  use  with  wire  armoured 
cables,  to  ensure  electrical  continuity  through  the 
joints,  but  these  clamps  would  be  omitted  in  the  event 
of  the  cables  being  unarmoured. 

When  electric  motors  are  used  in  the  mine  for 
operating  portable  machines,  such  as  coal  cutters, 
drills,  etc.,  they  are  connected  up  by  a  flexible 
conductor  technically  known  as  a  trailing  cable.  As 
many  accidents  which  occur  have  been  traced  to  the 
use  of  such  portable  machinery  and  trailing  cables, 
it  has  become  necessary  to  devote  special  attention 
to  the  subject.  The  conditions  are  exceptionally 


76  ELECTRICAL  MINING  INSTALLATIONS 

severe,  and  the  trailing  cable  is  often  dragged  over 
rough  places  where  sharp  projections  ,f.  are  met,  or 
subjected  to  damage  from  falls  of  roof  or  dropped 
tools.  Sometimes  the  cable  may  be  struck  by  a 
pick  or  shovel,  and  all  these  contingencies  have  to 
be  guarded  against. 

Trailing  cables  usually  embody  conductors  of 
fine  drawn,  high  conductivity,  tinned  copper  wires 
stranded  together  to  form  a  flexible  whole,  and 
insulated  with  pure  Para  and  vulcanized  indiarubber, 
the  radial  thickness  of  the  dielectric  being  greater 
than  that  usually  allowed  for  a  given  working  pressure. 
The  insulated  cores  are  then  laid  up  together  (two 
for  continuous  current  working  and  three  for  three- 
phase)  with  wormings  of  yarn  and  covered  overall 
with  a  flexible  protective  braid  or  armour. 

The  Home  Office  rules  require  trailing  cables  to 
be  specially  flexible,  heavily  insulated,  and  protected 
with  either  galvanized  steel  wire  armouring,  extra 
stout  braiding,  hose  pipe,  or  other  effective  covering. 
Among  cables  of  the  non-armoured  class  we  find 
protective  coverings  consisting  of — (a)  Mattress  twine 
braided  and  compounded ;  (b)  Hard  core  braid, 
specially  manufactured  to  prevent  unravelling  when 
cut ;  (c)  Compounded  hard  core  braid,  interlaced 
with  galvanized  steel  wires,  which  gives  a  smooth 
surface,  and  is  less  bulky  than  most  other  coverings  ; 
(d)  Haw  hide  or  leather  braid ;  (e)  Wrapping  of 
stout  marline  ;  (/)  Rubber  insulated  cables  drawn 
into  stout  rubber  hose  pipe  or  flexible  metallic 
tube.  In  some  cases,  for  continuous  current  working, 
two  separately  insulated  and  protected  cables  are 
employed,  laid  side  by  side  and  bound  together  at 
intervals  of  a  yard  with  stout  tarred  mattress  twine. 

With  the  above  non-metallic  form  of  protection 
there  is  no  question  of  earthing,  and,  as  a  matter 
of  fact,  the  Home  Office  rules  do  not  call  for  the 
earthing  of  portable  motors  or  trailing  cables,  even 
if  the  latter  be  armoured.  For  this  reason  one 


UNDERGROUND  CABLES  AND  FITTINGS    77 

of  the  most  serious  difficulties  colliery  engineers 
have  to  contend  with  is  the  risk  of  shock  owing  to  a 
portable  motor  becoming  alive.  It  is  difficult  to 
maintain  an  efficient  and  effective  earth  connexion 
with  machines  that  are  always  being  moved  about. 
Some  engineers  prefer  to  earth  their  machines  by 
means  of  a  wire  laid  up  in  the  flexible  trailing  cable, 
and  such  cables  are  provided  with  an  extra  core  for 
connecting  to  the  frame  of  the  motor,  this  core  being 
efficiently  earthed  at  another  point. 

The  Home  Office  rules  require  that  a  terminal 
box  shall  be  provided  at  all  points  where  flexible 
conductors  are  Joined  to  main  cables,  and  that  a 
switch  shall  be  fixed  close  to,  or  in  the  terminal 
box,  capable  of  entirely  cutting  off  the  supply  from 
the  terminal  box  and  motor.  These  terminal  boxes 
are  known  as  gate-end  boxes  and  it  is  essential  that 
they  be  properly  designed,  otherwise  there  is  risk  of 
accident.  The  three  essential  points  in  connexion 
with  the  design  of  a  satisfactory  gate-end  box  are  : — 

(a)  Easy  connexion  and  disconnexion  of  the  main 
cable  ;  (b)  Efficient  and  satisfactory  switch  and  fuse 
gear ;  (c)  Facilities  for  the  ready  connexion  and 
exchange  of  the  trailing  cable. 

Such  a  box,  designed  by  Messrs.  Callender,  is 
shown  in  Fig.  19,  and  it  will  be  noticed  that  the  main 
cable  is  brought  in  at  the  righthand  side,  and  the 
three  cores  connected  by  couplings  to  three  copper 
rods,  which  pass  through  glands  to  the  fuse  terminals 
in  the  main  chamber.  The  coupling  chamber  is 
provided  with  an  independent  lid,  which,  when  in 
position,  makes  an  airtight  joint  and  obviates  the 
use  of  compound.  The  main  chamber  contains  the 
switch  and  fuse,  the  former  being  operated  by  a 
removable  handle,  and  so  arranged  that  if  a  fuse 
blows  it  is  impossible  to  renew  it  with  the  switch 
"  on  " ;  further,  owing  to  special  interlocking  gear 
it  is  impossible  to  remove  the  lid  of  the  chamber 
before  first  opening  the  switch.  The  main  chamber 


78     ELECTRICAL  MINING  INSTALLATIONS 
is  filled  with  resin  oil  which  prevents  sparking  when 


FIG.   19.     CALLENDER'S  GATE-END  Box. 

a  fuse  blows.     The  trailing  ends  are  designed  for  rapid 
connexion  and  disconnexion  to  the  main  chamber ; 


but  owing  to  the  interlocking  arrangement,  the 
trailing  end  cannot  be  inserted  or  removed  unless 
the  switch  is  "  off,"  thus  making  it  impossible  to 
produce  a  spark  by  negligence  in  manipulating  the 
box. 

Another  type  of  gate-end  box  is  shown  in  Pig.  20 
and  is  designed  for  use  with  Fisher's  patent  protective 
system.  In  addition  to  the  requirements  above 
referred  to,  this  gate-end  box  has  several  automatic 
features,  designed  to  prevent  any  possibility  of 
accident,  even  in  the  hands  of  the  most  careless 
operator.  It  will  automatically  interrupt  the  supply 
in  the  event  of — (a)  Persistent  overload  ;  (b)  Short- 
circuit  between  phases  ;  (c)  A  fault  between  any 
phase  and  earth  ;  (d)  No  voltage  or  failure  of  supply  ; 
(e)  A  break  or  bad  contact  in  the  earth  circuit.  The 
gate-end  switch  cannot  be  closed  unless  the  earth 
connexion  is  complete,  and  it  may  be  opened  by 
operating  a  small  lever  attached  to  the  coal  cutter 
or  other  portable  machine. 

The  Fisher  system  involves  the  use  of  a  trailing 
cable  having  a  pilot  or  subsidiary  wire,  in  addition 
to  an  earth  conductor. 

The  gate-end  switch  is  controlled  by  a  solenoid 
in  circuit  with  the  pilot  and  earth  conductor,  so 
that,  if  the  earth  circuit  is  incomplete,  current 
cannot  pass  through  the  solenoid,  and  it  is  impossible 
to  close  the  switch. 

\  Fig.  20  shows  the  arrangement  for  a  three-phase 
supply  with  earthed  neutral. 

When  the  operating  switch  is  closed  (provided 
the  pilot  circuit  and  the  earth  conductor  are  com- 
pleted through  the  framework  of  the  machine),  the 
solenoid  P  is  energized  and  the  main  switch  closed. 
On  releasing  the  handle  of  the  control  switch,  the 
switch  springs  automatically  on  to  its  contact  which 
puts  a  high-resistance  solenoid  in  circuit,  and  also 
effects  a  change-over  by  which  the  connexion  through 
the  solenoid  is  taken  from  the  outgoing  side  of  the 


80     ELECTRICAL  MINING  INSTALLATIONS 

switch.     It  will  be  seen  that  the  main  switch  cannot 
be  held  in  the  closed  position  unless  current  passes 


through  the  solenoid,  and  there  will  be  no  circuit 
through  the  solenoid  unless  the  earth  circuit  is  com- 


UNDERGROUND  CABLES  AND  FITTINGS    81 

plete,  or  if  the  supply  voltage  fails.  By  this  means 
the  switch  opens  automatically  under  the  fault 
conditions  enumerated  above. 

8  is  a  three  pole  oil-break  switch  fitted  with  three 
overload  release  coils  R,  R,  R,  governed  by  a  time-lag 
device  of  the  oil  dash-pot  type.  A  scale,  Y,  is  pro- 
vided for  adjusting  the  setting  of  this  overload 
arrangement. 

P  is  the  controlling  solenoid,  and  has  two  windings, 
one  of  which  is  used  to  give  a  maximum  pull  at  the 
moment  of  closing  the  switch,  whilst  the  other  is  a 
coil  of  high  resistance,  consuming  only  the  small 
amount  of  energy  sufficient  to  hold  up  the  armature, 
when  the  switch  is  "  on,"  but  the  latter  is  knocked 
out  by  means  of  simple  mechanism,  when  the  weight 
of  the  armature  is  released  by  the  solenoid. 

F  is  a  small  control  switch,  operated  from  outside 
the  box  by  the  handle  G.  This  control  is  on  a  free 
handle  principle,  i.e.,  in  the  event  of  a  fault  occurring 
the  main  switch  is  bound  to  trip  out,  even  though 
the  control  switch  is  held  by  the  operator,  or  if  an 
attempt  be  made  to  tamper  with  the  device. 

L  is  an  indicating  lamp  which,  by  the  aid  of  a 
simple  shutter  device,  is  visible  through  a  strong 
glass  window,  and  gives  a  clear  indication,  which 
can  be  seen  from  outside,  whether  the  switch  is 
"  on "  or  "  off."  The  lamp  is  connected  to  the 
incoming  cable,  and,  when  no  light  is  seen  indicates 
that  the  supply  is  cut  off  from  this  source. 

The  overload  release  coils  R  and  R,  in  operating, 
open  the  control  circuit  and  so  release  the  main 
switch.  The  complete  mechanism  is  enclosed  in  a 
strong  iron  case.  The  current-breaking  parts  are 
immersed  in  oil.  The  case  and  lid  have  wide  machined 
joints  to  avoid  the  possibility  of  an  emission  of  flame. 
Mechanical  terminals  are  provided  throughout,  so 
that  joints  can  be  made  without  soldering.  Those 
at  A  take  the  incoming  cable,  the  insulated  ends  of 
which  are  located  in  a  box  which  can  be  run  in 


82     ELECTRICAL  MINING  INSTALLATIONS 

solid  with  compound  for  the  purpose  of  sealing  the 
ends.  Suitable  glands  are  provided  for  earthing 
the  armour  thoroughly  to  the  box.  The  trailing 
cable  is  attached  to  the  plug  B.  The  plug  is  enclosed 
in  a  strong  cast-iron  case,  and  is  so  interlocked  with 
the  control  switch,  that  it  is  impossible  to  withdraw 
the  plug  when  the  main  switch  is  closed.  This 
interlocking  is  effected  by  the  pawl  K,  and  it  is 
obviously  impossible  to  draw  out  an  arc  in  manipu- 
lating the  plug  because  the  latter  cannot  be  with- 
drawn when  the  circuit  is  alive.  A  corresponding 


Socket  for  Fitting 
to  Cutting  Machines, 


Plugs  For  use 
with  above. 

"  Trailing  Cable 
FIG.  21.     PLUG  ;  FISHER  PATENT  SYSTEM. 

plug  is  used  at  the  coal-cutter  end  of  the  trailing 
cable,  and  a  socket  is  made,  as  shown  in  Fig.  21 
suitable  for  fixing  to  any  existing  coal-cutter  frame. 
Like  the  corresponding  socket  on  the  gate-end  box, 
it  carries  a  locking  pawl  inter-connected  with  a  small 
switch,  by  which  the  men  working  the  coal-cutter 
can  open  the  control  circuit,  and  so  render  the  trailer 
and  motor  dead,  and  ensure  that  they  cannot  be 
again  energized  until  the  switch  is  closed  at  the  coal- 
cutter end.  The  system  enables  a  supply  to  be 
cut-off,  right  back  to  the  gate-end  box,  and  not  only 
disconnects  the  motor,  but  the  trailing  cable  as  well, 


UNDERGROUND  CABLES  AND  FITTINGS    83 

and  at  the  same  time  prevents  any  one  accidentally 
closing  this  circuit  if  the  men  at  the  coal-cutter  are 
carrying  out  any  work  on  the  machine. 

The  plug  is  made  reversible  so  that  the  motor  can 
be  reversed,  if  necessary,  by  simply  withdrawing 
the  plug  and  reinserting  it  the  other  way  round. 

It  is  obvious  that,  if  the  plug  is  not  in  the  socket, 
the  control  circuit  is  incomplete,  and  it  is  thus 
impossible  to  close  the  main  switch  with  the  plug 
lying  on  the  ground. 

In  reference  to  the  question  of  earthing  cable 
systems  generally,  it  wi]l  be  noticed  that  the  Home 
Office  rules  do  not  enforce  this  for  medium  pressure, 
although  it  is  insisted  upon  for  high  pressure  working. 
It  is  quite  an  open  question  at  the  present  time  with 
colliery  engineers,  and  some  prefer  unarmoured 
cable  for  use  underground.  In  some  respects  this 
unarmoured  unearthed  cable  is  safer,  if  the  installa- 
tion is  improperly  maintained.  When  a  fault  occurs 
in  an  unarmoured  cable,  a  severe  shock  can  only  be 
experienced  at  the  actual  fault,  and,  further,  one  may 
have  a  serious  fault  on  one  or  more  cables,  and  still 
be  able  to  run  without  danger  to  life  or  property. 

With  metallic-armoured  cables  this  would  be 
impossible,  because  if  an  armoured  cable  be  faulty 
the  armouring  is  at  the  same  potential  as  the  con- 
ductor ;  if  the  armouring  is  connected  to  earth  this 
can  never  be  more  than  a  few  volts  above  earth 
potential.  If,  on  the  other  hand,  the  armouring  is 
not  earthed,  or  if  the  earth  connexion  is  faulty 
the  pressure  may  be,  say,  500  volts  above  earth  poten- 
tial, not  only  at  the  actual  fault  but  all  along  the 
armouring.  This  is  of  course  exceedingly  dangerous 
and  effective  earthing  is  the  only  practical  way  of 
avoiding  danger  when  armoured  cables  are  used. 

The  armouring  must  not  only  be  efficiently  earthed 
but  care  must  be  taken  to  make  it  electrically  con- 
tinuous throughout.  To  this  end  all  joint  boxes 
should  be  arranged  for  clamping  the  armour  as 


84    ELECTRICAL  MINING  INSTALLATIONS 

shown  in  Figs.  16,  17  and  18.  In  important  installa- 
tions it  is  sometimes  the  practice  to  lay  an  earth 
wire,  or  strand  of  copper  wires,  along  the  cable  route 
and  connect  to  it  all  the  cable  armouring  as  well  as 
motor  frames  and  auxiliary  apparatus.  This  ar- 
rangement has  great  advantages  over  the  ordinary 
system  of  earthing  by  way  of  the  armouring  only, 
since  a  break  in  a  supply  cable  will  be  insufficient  to 
destroy  the  earth  connexion,  and,  further,  the  earth 
connexion  of  any  particular  section  may  be  broken 
without  affecting  that  of  the  remainder. 

In  connexion  with  the  application  of  electricity 
for  lighting  in  collieries,  it  will  only  be  necessary  to 
deal  with  a  few  special  points.  The  subject  of  elec- 
tric lighting  is  a  broad  one,  and  the  reader  is  referred 
to  other  volumes  in  this  series  for  details,  both  in 
connexion  with  arc  and  incandescent  lighting. 

The  Home  Office  regulations  require  that  all  arc 
lamps  shall  be  so  guarded  as  to  prevent  pieces  of 
incandescent  carbon  falling  from  them,  and  shall 
not  be  used  in  situations  where  there  is  likely  to  be 
danger  owing  to  the  presence  of  coaldust.  They 
should  be  so  screened  as  to  prevent  risk  of  contact. 

Small  wires  for  lighting  circuits  must  be  either 
carried  in  pipes  or  casings,  suspended  from  porcelain 
insulators,  or  tied  to  them  with  some  non-conducting 
material  which  will  not  cut  the  covering,  and  in  such 
manner  that  they  do  not  touch  any  timbering  or 
metal  work.  On  no  account  must  staples  be  used. 
If  metallic  pipes  are  used  they  must  be  electrically 
continuous  and  earthed.  If  separate  uncased  wires 
are  used  they  must  be  kept  at  least  2  in.  apart,  and 
not  brought  together  except  at  lamps,  switches,  or 
fittings. 

In  any  place  or  part  of  a  mine  to  which  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  electric  lamps,  if  used,  must  be  of  the  vacuum 
or  enclosed  type  ;  they  must  be  protected  by  gastight 
fittings  of  strong  glass,  have  no  flexible  cord  cqnnex- 


UNDERGROUND  CABLES  AND  FITTINGS    86 

ions,  and  must  only  be  changed  by  a  duly  authorized 
competent  person.  While  the  lamps  are  being 
changed  the  current  must  be  switched  off. 

The  electric  lighting  of  surface  works  does  not 
call  for  any  special  comment.  Electric  lighting 
underground,  by  means  of  incandescent  lamps,  may 
be  arranged  on  the  three-wire  continuous-current 
system  if  the  pressure  lies  between  250  and  500  volts, 
care  being  taken  to  distribute  the  lighting  between 
the  two  sides  of  the  system  as  equally  as  possible. 

With  three-phase  working  a  step-down  transformer 
would  be  used  to  obtain  the  most  suitable  pressure 
for  lighting  purposes.  A  three-phase  step-down 
transformer  for  this  purpose  should  be  mesh  con- 
nected on  the  primary  side  as  shown  in  Fig.  5  (b) 
and  star-connected  on  the  secondary  side  as  in  Fig. 
5  (c)  the  lighting  circuits  being  arranged  between 
the  neutral  and  each  outer  or  line  wire.  From  such 
a  three-phase  transformer  it  will  therefore  be  neces- 
sary to  have  three  distributing  circuits,  and,  although 
a  perfect  balance  is  not  absolutely  necessary,  care 
should  be  taken  to  divide  the  load  between  the  three 
circuits  as  equally  as  possible. 

A  transformer  with  mesh-connected  primary  and 
star-connected  secondary  is  recommended,  because 
this  arrangement  gives  better  balancing,  but  a  cheaper 
combination  may  be  used,  consisting  of  an  auto- 
transformer  with  star  connexions,  the  main  supply 
being  connected  to  the  outer  terminals,  and  tappings 
provided  on  each  limb,  from  which  the  low-tension 
current  may  be  taken  for  lighting  purposes.  This 
arrangement  is  not  so  good  from  a  balancing  point 
of  view,  and,  if  adopted,  special  care  must  be  taken 
to  distribute  the  lighting  over  the  three  single-phase 
circuits  as  equally  as  possible. 

In  employing  alternating  current  for  lighting 
purposes  it  must  be  remembered  that,  with  low 
frequencies,  there  may  be  trouble  due  to  fluctuation 
in  the  lights.  Arc  fighting  cannot  be  successfully 


86     ELECTRICAL  MINING  INSTALLATIONS 

carried  out  on  a  lower  frequency  than  40  cycles  per 
second.  Incandescent  lighting  is  satisfactory  with 
a  frequency  as  low  as  25  cycles  per  second  for  mine 
work,  but  low  voltages  (100-110  volts)  are  recom- 
mended, in  order  that  the  lamp  filaments  may  be 
thick  and  short.  The  amount  of  fluctuation  on 
low  frequencies  is  less  with  a  lamp  having  a  short 
thick  filament. 


CHAPTER    VI 
ELECTRIC  HAULAGE 

ONE  of  the  great  advances  in  recent  mining  practice 
is  the  adoption  of  electric  haulage,  and  in  many 
cases  this  has  become  an  absolute  necessity  in  order 
to  remove  coal  from  the  working  faces  and  deliver 
it  in  the  quantities  required. 

There  are  three  distinct  systems  of  haulage,  known 
as  (a)  main  rope  haulage,  (b)  main  and  tail  haulage, 
and  (c)  endless  rope  haulage  (apart  from  the  con- 
sideration of  traction  by  locomotive),  and  the  selection 
of  any  particular  system  depends  entirely  upon 
circumstances. 

The  main  rope  haulage  usually  consists  of  one 
drum,  winding  a  single  rope,  and  hauling  the  tubs 
up  the  gradient.  This  type  of  haulage  gear  can 
obviously  only  be  used  on  roads  having  a  continuous 
down  gradient  in  the  direction  away  from  the  gear, 
since  the  tubs  are  required  to  run  back  by  gravity. 

Fig.  22  shows  a  typical  arrangement  of  this  type 


FIG.  22.     PLAN  or  MAIN  HAULAGE  GEAR. 


- 


88     ELECTRICAL  MINING  INSTALLATIONS 

of  gear  which  is,  perhaps,  the  simplest.  The  motor 
usually  drives  through  double  reduction  spur-gear, 
on  to  the  drum  shaft,  and  as  it  is  usual  to  start  up 
the  motor  by  means  of  a  controller,  no  friction  clutches 
need  be  employed,  but  these  are  sometimes  included 
if  the  starting  conditions  are  severe,  and  in  any  case 
a  clutch  of  the  friction,  or  claw,  type  must  be  fitted 
for  the  purpose  of  disengaging  the  drum  from  the 
shaft,  and  allow  the  load  to  run  back  by  gravity.  It 
is  not  considered  necessary  to  reverse  the  motor 
with  this  type  of  haulage,  although,  as  explained 
later  on,  reversing  controllers  are  often  employed. 
A  substantial  brake  gear  must  of  course  be  fitted, 
capable  of  holding  the  maximum  load  on  the  incline. 

The  use  of  this  type  of  haulage  gear  obviously 
depends  upon  the  gradient  of  the  roads,  which 
should  be  at  least  3  inches  per  yard  for  the  system 
to  work  satisfactorily,  although  if  the  rails  are  light, 
and  badly  laid,  it  may  be  necessary  for  the  gradient 
to  be  even  steeper,  to  ensure  satisfactory  working. 

In  many  instances  it  is  impossible  to  obtain  a 
continuous  down  grade  in  a  direction  away  from  the 
haulage,  in  which  case  the  empty  tubs  cannot  return 
by  gravity,  and  a  tail  rope  has  to  be  employed  for 
the  purpose  ;  haulage  gear  arranged  on  this  principle 
is  known  as  "  main  and  tail  "  haulage.  The  arrange- 
ment usually  consists  of  two  drums  as  shown  in 
Fig.  23,  one  winding  the  main,  and  the  other  the 
taS  rope.  With  this  arrangement  clutches  are  not 
absolutely  necessary,  although  they  may  be  employed 
if  the  starting  conditions  are  severe,  but  in  most 
cases  the  motor  is  provided  with  a  reversing  con- 
troller, capable  of  starting,  stopping,  reversing,  and 
regulating  the  motor  according  to  requirements. 
Brakes  are  fitted  as  usual. 

The  disadvantage  of  main  and  tail  and  also  of 
main  rope  haulage  is  the  time  lost  in  working.  On 
consideration  it  will  be  seen  that,  allowing  time  for 
the  return  of  the  empty  tubs,  and  also  for  changing 


ELECTRIC  HAULAGE 


89 


the  tubs  at  each  end  of  the  run,  the  motor  is  only 
effectually  working  for  about  one-third  of  the  total 
time.  In  cases,  therefore,  where  time  is  important, 
and  it  is  required  to  haul  the  maximum  amount  of 
material,  a  haulage  of  the  endless  rope  type  is  used. 
With  this  gear  two  ropes  (which  form  one  endless  loop) 
run  continuously,  the  full  tubs  travelling  up  on  the 
one  rope  and  the  empty  tubs  returning  by  the  other, 
the  gear  running  continuously  for  long  periods. 
This  system  is  very  simple,  but  the  roads  must  be 


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MAIN  AND  TAIL  HAULAGE  GEAR. 

fairly  straight  and  also  wide  enough  for  the  two 
lines  of  tubs  to  pass.  Other  advantages  of  this  type 
•of  gear  are  that  the  material  is  delivered  more  regu- 
larly, and  the  power  required  to  drive  may  be  less, 
owing  to  the  fact  that  the  full  and  empty  tubs  tend 
to  balance ;  further,  owing  to  the  comparatively 
slow  speed  at  which  the  rope  travels,  the  rails  may 
be  lighter  than  with  main  haulage  or  main  and  tail 
haulage  gears. 

Endless  rope  haulage  gear  is  often  made  in  a  form 
similar  to  main  haulage  with  single  drum,  this  drum 
being  of  special  shape  with  the  rope  passing  round 
three  or  four  times  to  ensure  sufficient  grip.  Many 


90     ELECTRICAL  MINING  INSTALLATIONS 

types  of  drum  have  been  designed  for  endless  rope 
haulage  gears,  and  in  some  cases  a  single  grooved 
pulley  is  used. 

The  motors  operating  this  type  drive  through 
single  or  double  reduction  gearing  as  usual  on  to  the 
drum  shaft,  but  the  motor  is  not  required  to  reverse, 
although  a  reversing  controller  is  often  supplied  in 
connexion  with  such  equipments.  Occasionally  haul- 
ages are  designed  with  two,  three,  or  even  four  rope 
drums,  or  wheels,  for  operating  ropes  on  as  many 
different  routes.  In  this  case  the  motor  and  gear 
run  continuously,  and  any  drum  or  wheel  may  be 
set  in  motion  or  stopped  by  a  suitable  friction  clutch, 
efficient  brakes  being  also  provided  on  each  drum. 

In  regard  to  haulage  gears  generally,  the  motors 
must  be  rated  according  to  the  requirements  of  each 
particular  case,  but  broadly  speaking,  the  following 
are  usually  considered  correct. 

Main  rope  haulage  .          .     Motor   of  one  hour  rating. 

Main  and  tail  rope  haulage  .  Motor  of  two  hour  rating. 
Endless  rope  haulage  .  .  Motor  of  continuous  rating. 

By  thus  rating  the  motors  in  hours,  we  mean  that 
the  temperature  rise  must  not  exceed  a  certain 
specified  figure,  say,  75°  F.,  after  a  run  at  normal 
full-load  for  the  periods  stated. 

With  continuous  rated  motors  a  period  of  six 
hours  is  usually  considered  sufficient  for  the  purpose 
of  a  temperature  test. 

The  reason  for  adopting  motors  of  one  or  two  hour 
rating  is  because  such  machines  are  only  required 
to  run  for  short  periods  at  their  rated  load.  In  the 
case  of  a  main  haulage  gear,  the  motor  will  run  for 
a  "period  at  its  full  rated  load,  and  then  remain 
stationary,  whilst  the  tubs  return  by  gravity. 

In  the  case  of  the  main  and  tail  haulage  gear  the 
motor  will  work  for  a  period  at  its  full  rated  load, 
then  at  a  much  smaller  load  when  returning  the 
empty  trucks,  and  will  remain  stationary  for  some 
time  while  the  tubs  are  changed. 


ELECTEIC  HAULAGE  91 

If  the  motors  operating  the  haulages  are  of  the 
continuous-current  variety,  they  are  usually  series 
wound,  in  order  to  obtain  the  maximum  starting 
torque,  but  in  other  cases,  such  as  endless  rope  haulage 
gears,  operating  no  more  than  one  rope,  it  is  prefer- 
able to  fit  compound-wound  motors  in  order  that 
the  speed  may  be  maintained  constant  at  all  loads, 
a  disadvantage  of  the  series  motor  being  that  the 
speed  increases  on  light  load.  If  the  supply  is  three- 
phase  alternating,  the  haulage  motors  will  be  of  the 
wound  rotor  type,  with  slip  rings. 

As  regards  the  controlling  equipment,  it  is  usual 
to  put  in  controllers  of  the  tramway  type,  suitable 
for  starting,  regulating,  and  reversing.  Such  con- 
trollers are  of  the  non-automatic  type,  for  hand 
operation  only,  a  suitable  panel  being  also  provided 
with  automatic  switches,  having  overload  and  no- 
volt  attachments  if  necessary,  together  with  such 
instruments  as  may  be  required. 

Controllers  for  continuous-current  motors  are 
usually  of  the  vertical  tramway  pattern,  and  are 
fitted  with  magnetic  blow-outs  to  reduce  sparking  to 
a  minimum. 

For  alternating  current  motors  they  may  be  of 
the  above  type  when  used  in  connexion  with  small 
machines,  although,  for  obvious  reasons,  magnetic 
blow-outs  are  in  such  case,  impracticable. 

With  large  three-phase  alternating  current  motors 
it  is  usual  to  employ  oil  immersed  controllers,  in 
order  that  the  heavy  current  may  be  handled  without 
burning  and  arcing  at  the  contacts. 

These  oil  immersed  controllers  may  be  of  vertical, 
but  are  more  often  made  in  horizontal  form,  as  this 
makes  a  better  arrangement  for  the  connecting  cables, 
while  the  controller  can  be  so  arranged  that  the  tank 
may  be  lowered  for  inspection  when  necessary. 
Such  controllers  can  be  provided  with  a  handle  or 
hand  wheel,  while,  in  the  case  of  very  large  haulage 
controllers,  signal  levers  may  be  adopted,  and  are 


92    ELECTRICAL  MINING  INSTALLATIONS 

placed  in  a  convenient  position  on  the  bed  of  the 
haulage  gear  within  easy  reach  of  the  attendant. 
In  fiery  mines  it  is  absolutely  necessary  to  employ 
oil  immersed  controllers,  in  order  that  there  may  be 
no  risk  of  explosion  set  up  by  arcing  at  the  contacts. 

Controller  resistances  for  haulage  work  usually 
take  the  form  of  cast-iron  grids  made  up  in  units, 
which  are  often  left  open,  but  protecting  covers  may 
be  provided  when  required. 

The  resistances  are  designed  for  starting  and 
regulating,  and  the  usual  practice  is  to  allow  for  50 
per  cent,  speed  regulation  over  periods  of  ten  to 
fifteen  minutes,  without  undue  heating  or  damage. 
In  special  cases  the  resistances  are  also  designed  to 
give  a  creeping  speed. 

Reversing  controllers  are  usually  employed  inde- 
pendent of  whether  the  hauling  gear  is  of  the  main 
and  tail  or  endless  rope  type,  and  even  for  main  haul- 
ing gears  where  no  tail  rope  is  employed.  Although 
endless  rope  gears  are  seldom  required  to  reverse, 
and  main  gears  are  reversed  by  running  the  load  out 
on  the  brake,  it  may  still  be  necessary  at  some  time 
or  another  to  reverse  the  motor  quickly,  as  in  the 
event  of  a  truck  getting  off  the  line  or  a  rope  jamming. 
At  the  same  time  a  reversing  costs  no  more  than  a 
non-reversing  controller,  and,  for  the  above  reasons, 
it  is  standard  practice  to  employ  controllers  with  a 
reversing  motion,  irrespective  of  the  type  of  gear  in 
connexion  with  which  they  are  to  be  used. 

A  few  engineers  prefer  liquid  starting  resistances 
for  haulage  gears,  with  the  reversing  contacts  on  the 
apparatus,  or  embodied  in  a  changeover  triple-pole 
oil-break  switch,  interlocked  with  the  liquid  con- 
troller. While  this  arrangement  is  cheap  for  large 
gears,  and  has  other  advantages,  it  is  very  seldom 
employed,  and  is  not  standard  practice  in  this  country. 

The  switch  panels  required  in  connexion  with  each 
haulage  gear  will  usually  consist  of  an  automatic 
switch,  fitted  in  iron  case,  and,  if  the  power  be  more 


ELECTRIC  HAULAGE 


93 


than  10  B.H.P.,  an  ammeter  must  be  provided  in 
accordance  with  Home  Office  rules. 

In  some  special  cases  of  very  large  haulage  gears, 
it  has  been  found  impracticable  to  use  the  standard 
form  of  motor,  and  controller,  owing  to  the  severe 


Series  Wound  Motor 


Resistances 


Series  \Field 


[  O  ]  Armature 


Line 


Compound  Wound  Motor 


Line 

B 

Non 

P                                  JjJ 

Resistffncfs  c*   ."—  •  -   »                MI 

P                                 ** 

^? 

Inductive  C                                            ^ 

Resistance      \ 

4 

Line 

FIG.  24.     REVEBSESTG  CONTROLLER  FOR  CONTINUOUS   CUR- 
RENT MOTORS. 

conditions  ;  in  such  cases  haulage  gears  are  arranged 
on  a  system  very  similar  to  that  described  for  main 
winding. 

In  other  cases  large  haulage  gears   have  to   be 
designed  to  meet  special  circumstances,  and  we  may 


94    ELECTRICAL  MINING  INSTALLATIONS 

find  more  than  one  motor  operating  with  series 
parallel  control,  in  the  case  of  continuous  current ; 
or  cascade  control  in  the  case  of  three-phase  systems. 
It  may  sometimes  be  necessary,  owing  to  the  great 
distances  over  which  electrical  energy  has  to  be  trans- 
mitted, to  wind  haulage  motors  for  high  tension 
working,  in  which  case  special  precautions  must  be 
taken  in  regard  to  the  protection  and  control  of  such 

LLL  Forward  Reverse 

( 


FIG.  25.     THREE-PHASE  REVERSING  CONTROLLER. 


machines  ;  but  the  Home  Office  rules  stipulate  that 
no  high  tension  motor  of  less  than  20  H.P.  may  be 
used  underground. 

Diagrams  of  connexions  for  continuous  and 
alternating  current  controllers  are  shown  in  Figs.  24 
and  25  respectively.  Fig  24,  A,  shows  the  connexions 
for  a  series-wound,  and  Fig.  24,  B,  the  arrangement 
for  a  compound-wound  motor.  The  connexions  in 
Fig.  25  assume  the  combination  of  a  three-phase 


ELECTRIC  HAULAGE  95 

motor  with  a  three-phase  rotor,  but  in  some  cases  a 
two-phase  rotor  may  be  used. 

In  designing  haulage  gears,  makers  have  to  take 
into  account  the  maximum  strains  to  which  they  are 
likely  to  be  subjected,  but,  in  calculating  the  horse- 
power required  to  drive,  we  take  an  average  of  the 
power  required  over  a  complete  cycle  of  operations. 
The  power  required  will  naturally  depend  upon  the 
load,  and  the  gradient ;  it  will  also  depend  upon  the 
speed  and  condition  of  the  load,  losses  in  gearing 
and  loads,  and  upon  the  type  of  gear  in  question. 
As  a  rule  the  quantity  of  material  to  be  handled  is 
definitely  known,  and  this  determines  the  load.  The 
gradient  is  also  fixed,  so  that  the  speed,  together 
with  the  type  of  gear,  are  the  only  items  that  remain 
to  be  settled.  Assuming  that  all  these  points  have 
been  decided  it  is  a  comparatively  easy  matter  to 
calculate  the  B.H.P.  required. 

In  regard  to  speed  it  may  be  mentioned  that  6 
miles  per  hour  is  usual  for  main  haulage  or  main  and 
tail  haulage  gears,  and  even  greater  speeds  are  some- 
times attained  in  the  case  of  large  sets.  For  endless 
rope  haulage  2-4  miles  per  hour  is  usual,  although  it 
depends  upon  weight  of  rail,  and  condition  of  road. 
If  the  former  be  heavy,  and  the  road  good,  a  higher 
speed  can  be  employed  than  with  light  rails  and  a 
badly  laid  road. 

Although  the  power  required  may  be  calculated 
to  a  nicety  from  the  following  formula,  a  certain 
amount  of  reserve  should  be  allowed  for,  and  the 
maximum  not  cut  too  fine.  Overloads  are  bound  to 
occur  when  one  or  more  tubs  are  derailed. 

In  fixing  the  voltage  of  haulage  motors  allowance 
must  also  be  made  for  loss  in  pressure  due  to  trans- 
mission, especially  if  machines  are  placed  at  some 
considerable  distance  from  the  generating  station. 
It  must  be  remembered  that  the  speed  of  the  con- 
tinuous current  motor  falls  practically  in  proportion 
to  decrease  in  voltage,  although  the  torque  remains 


96     ELECTRICAL  MINING  INSTALLATIONS 

constant.  With  three-phase  motors,  however,  the 
torque  varies  directly  as  the  square  of  the  voltage, 
while  the  speed  of  the  machine  remains  constant. 

As  an  example,  let  us  take  the  case  of  a  main 
haulage  gear,  designed  to  work  under  the  following 
conditions — 


Nett  load 

Nine  tubs  at  15  cwts.  each 

Length  of  road 

Incline  of  road 

Speed      .... 

Haulage  rope  circumference 

Haulage  rope  weight 


12  tons  =  26,880  Ib. 
6J  tons=  15,121  Ib. 
800  yds. 

1  in.  per  foot  or  TV 
5  miles  per  hour. 

2  in. 

2J  Ib.  per  yd. 


For  single  drum  working  there  is  only  one  rope, 
and  the  pull  due  to  weight  and  friction  of  the  rope 
varies  from  a  maximum  to  zero  as  the  set  is  being 
hauled  up.  The  average  pull  is  obtained  by  consider- 
ing the  set  as  being  half-way  up  the  road,  that  is  to 
say,  400  yds.  from  the  drum.  The  friction  of  the 
load  is  taken  as  40  ]b.  per  ton,  and  that  due  to  the 
rope  as  10  per  cent,  of  its  weight. 

On  this  basis  it  will  be  easily  seen  that  the  total 
pull  on  the  rope  is  made  up  as  follows — 

Pull  due  to  load  26,880  x  TV  =          .          .  2,240  Ib. 

Pull  due  to  tubs  15,120  x  TV  =         .          .  1,260  Ib. 

Pull  due  to  rope  400  x[2J  x  TV  =     •          .  75  Ib. 

Friction  due  to  load  at  40  Ib  per  ton  =  480  Ib. 

Friction  due  to  tubs  at  40  Ib.  per  ton  =  270  Ib. 

Friction  due  to  ropes  400  x  2J  x  T\J%        •  90  Ib. 


Total  pull  on  rope  .          .          .        4,415  Ib. 

Then  the  power  required,  assuming  a  speed  of  5 
miles  per  hour  (440  ft.  per  minute)  =  4,415  X  440 
-T-  33,000  =  59  H.P.  Allowing  74  per  cent,  as  overall 
efficiency  of  haulage  gear,  we  obtain  80  B.H.P., 
which  will  be  required  for  the  motor,  and,  following 
the  usual  practice,  we  should  employ  a  motor  of  this 
output,  and  of  one  or  two  hour  rating. 

The  case  of  the  main  and  tail  haulage  gear  is  very 
similar,  but  to  make  matters  quite  clear  we  will  take 


ELECTRIC  HAULAGE  97 

another  example,  of  a  main  and  tail  haulage  gear, 
designed  to  work  unde  r  the  following  conditions — 


Nett  load. 

20  tubs  at  20  cwts.  each 

Length  of  road 

Incline  of  road 

Speed 


Haulage  rope  circumference     2  in. 


Haulage  rope  weight 
Length  of  rope 


15  tons  =  33,600  Ib. 

20  tons  =  44,800  Ib, 

1,500  yds. 

Level. 

6  miles  per  hour. 


2J  Ib.  per  yd. 

1,500  x  2  =  3,000  yds. 


With  main  and  tail  haulage  it  is  a  little  difficult 
to  decide  what  allowance  to  make  for  the  rope 
when  the  load  is  on  varying  gradients.  Assuming 
the  road  to  be  level,  however,  there  is  no  difficulty, 
as  it  is  quite  clear  there  will  always  be  a  full  quantity 
of  rope  lying  along  the  road,  both  main  and  tail,  or 
perhaps  all  tail,  and  friction  must  be  allowed  for 
accordingly ;  this  is  taken  as  10  per  cent,  of  the 
weight  of  the  rope. 

Working  on  this  basis  we  obtain  the  following 
values  for  the  pull  on  the  rope  due  to  above  load — 

Pull  due  to  load  (level)              .          .  0 

Pull  due  to  tubs  (level)    .          „          .  0 

Friction  due  to  load  at  40  Ib.  per  ton  600  Ib. 

Friction  due  to  tubs  at  40  Ib.  per  ton  800  Ib. 

Friction  due  to  ropes,  3,000  x  2J  x  -fife  865  Ib. 

Total  pull  on  rope       *.  ,         f.          .   2,265  Ib. 

Then  the  power  required,  assuming  a  speed  of  6 
miles  per  hour  (528  ft.  per  minute)  =  2265  X  528 
-5-  33,000  —  36-3  H.P.  Allowing  73  per  cent,  as 
overall  efficiency  of  haulage  gear,  we  obtain  50  B.H.P. 
which  will  be  required  for  the  motor,  and  in  accord- 
ance with  usual  practice  we  should  adopt  a  motor 
of  two  hour  rating. 

The  calculation  of  endless  rope  haulages  will  be 
very  similar  to  the  above,  but  due  allowance  must  be 
made  for  the  returning  tubs ;  the  pull  on  the  rope,  due 
to  gravity,  will  be  equalized.  The  motor  in  this 
case  must  of  course  be  continuously  rated. 


98   ELECTRICAL  MINING  INSTALLATIONS 

In  order  to  arrive  at  the  power  required  for  dealing 
with  any  quantity  of  coal  in  a  given  time,  by  means 
of  main  and  tail  or  endless  rope  haulage  gears,  the 
author  has  obtained  pei  mission  to  reproduce  the 
following  tables,  prepared  by  Mr.  W.  C.  Mountain. 

Table  I  gives  the  power  required  for  main  and  tail 
haulage  gears,  on  gradients  varying  from  2  in.,  in 
favour  of,  to  12  in.  in  the  yard,  against  the  load,  and 
this  table  may  be  taken  as  representing  the  actual 
horse-power  which  will  be  required  under  ordinary 
conditions,  with  a  proper  allowance  to  cover  friction. 
The  load  in  tons  includes  the  weight  of  tubs,  coal, 
and  rope. 


TABLE   I 

H.P.  REQUIRED  FOR  MAIN  AND  TAIL  HAULAGE  AT 
10  MILES  PER  HOUR. 


Actual 
Incline 
in 
Inches 
Per  Yd. 

Virtual 
Incline 
in 
Inches 
Per  Yd. 

LOAD  IN  TONS. 

5 

7-5 

10 

15 

20 

25 

30 

35 

4U 

45 

50 

-2 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

-1 

1 

8-3 

12-5 

16-6 

25 

33-2 

414 

50 

58 

664 

76 

80-8 

0 

2 

16-7 

25 

33-3 

50 

66-6 

83 

100 

116 

133 

150 

160 

1 

3 

25 

37-7 

50 

75 

100 

125 

150 

175 

200 

225 

250 

2 

4 

33-4 

50 

67-5 

100 

134 

167 

200 

233  270 

300 

334 

3 

5 

41-5 

62 

83-5 

125 

167 

208 

250 

290 

334 

375 

416 

4 

6 

50 

75 

100 

150 

200 

250 

300 

350 

400 

450 

500 

5 

7 

58-3 

87 

117 

175 

234 

294 

350 

408 

468 

525 

588 

6 

8 

66-3 

100 

133 

200 

267 

333 

400 

465 

532 

600 

666 

7 

9 

75 

112 

150 

225 

300 

375 

450 

520 

600 

675 

750 

8 

10 

83-5 

124 

166 

250 

333 

420 

500 

580 

664 

750|  830 

9 

11 

91 

137 

183 

275 

366 

459 

550 

640 

732 

825  918 

10 

12 

99 

150 

200 

300 

400 

500 

600 

696 

800 

900  1000 

11 

13 

108 

162 

217 

325 

433 

542 

650 

755 

868 

9751080 

12 

14 

116 

174 

233 

350 

466 

584 

700 

815 

932 

1050 

1168 

ELECTKIC  HAULAGE 


ill! 


100     ELECTRICAL  MINING  INSTALLATIONS 

With  main  rope  haulage  it  is  necessary  to  take 
the  weight  of  the  main  rope  only,  but  in  main  and 
tail  haulage,  the  weight  of  both  ropes  should  be  added 
to  that  of  the  coal  and  tubs  on  the  incoming  journey. 

It  will  be  noted  that  the  power  is  reckoned  at  a 
speed  of  10  miles  per  hour,  but,  by  taking  off  the 
figure  on  the  right,  or  introducing  a  decimal  point, 
the  table  at  once  gives  the  horse-power  required  at 
a  speed  of  one  mile  per  hour,  and  if  this  be  multiplied 
by  the  actual  speed  at  which  the  train  is  running, 
the  actual  horse-power  necessary  will  be  arrived 
at. 

In  calculating  horse-powers  for  main,  or  main  and 
tail  haulage,  the  length  of  the  road  is  not  taken  into 
account. 

Table  II.  Endless  Rope  Haulage. — With  endless 
rope  haulage,  where  tubs  are  attached  to  the  rope 
at  regular  intervals,  it  is  sufficient  to  take  the  delivery 
in  Ib.  of  coal  per  minute  at  the  pit  bottom,  or  to 
whatever  point  the  haulage  rope  is  required  to  deliver 
its  load,  and  it  will  be  noted  that  Table  II  gives  the 
horse-power  required  on  a  road  1,000  yds.  long,  from 
a  gradient  2  in.  to  the  yd.  in  favour  of,  to  12  in.  to  the 
yd.  against,  the  load. 

In  considering  the  horse-power  of  an  endless  rope 
haulage,  it  is  only  necessary  to  take  the  average 
gradient,  so  that,  if  the  total  length  of  the  road  be 
known,  and  the  total  rise,  this  will  at  once  give  the 
gradient,  in  inches  per  yd.,  against  which  the  load 
has  to  be  drawn. 

Mi  Assuming  the  road  is  more  or  less  than  1,000  yds. 
long,  the  horse-power  is  proportional  to  its  length. 
For  instance,  if  the  road  is  500  yds.  long,  the  horse- 
power required  will  be  one-half  that  shown  in  the 
table ;  if  twice  the  length,  then  double. 

Mr.  W.  C.  Mountain  has  made  a  comparison  of  the 
two  systems  of  haulage  as  regards  power  required, 
based  upon  the  above  tables,  and  the  following  ex- 
amples will  explain  the  application  of  the  rules,  assum- 


ELECTETO 


ing  that  the  work  to  be^done  fty  each  haulage  is  as 
follows  :  — 

Capacity  in  10  hours  .          .  600  tons. 

Capacity  per  hour        .          .  60  tons. 

Capacity  per  minute    .          .  1  ton. 

Length  of  road,   1,760  yds.  1  mile. 

Gradient  against  load  .  4  in.  to^the  yd. 

Weight  of  each  empty  tub  4  cwts. 
Weight  of  coal  per  tub     ,  .            ,    10  cwts. 

The  power  required  for  main  and  tail  haulage  will 
therefore  be  as  under  :<  — 


Number  of  trains  per  hour   . 

Time  allowed  for  hauling  both 

tubs  outbye       .          .         f 

Time     allowed     for     hauling 

empty  tubs  inbye 
Hitching   on   full  and  empty 
tubs  .... 

Total  time  per  journey  in  and 

out 

Number  of  tubs  per  journey 
Capacity,   10  cwts.  each 
Weight  of  tubs,  4  cwt.  each 
Estimated  weight  of  rope 
Total  weight  of  train,  includ- 
ing coal,  tubs  and  rope     . 
Speed  of  haulage 


3, 

8  minutes. 
8  minutes. 
4  minutes. 

20  minutes. 

40. 

400  cwt.  or  20  tons. 

160  cwt.  or  8  tons. 

40  cwt.  or  2  tons. 


30  tons. 

1  mile  in  8  minutes. 

or  7J  miles  per  hour. 

From  the  main  and  tail  haulage  Table  I  it  will  be 
seen  that,  if  a  load  of  30  tons  is  to  be  hauled  up  a 
gradient  of  4  in.  to  the  yd.  against  the  load,  at  a  speed 
of  10  miles  yer  hour,  300  H.P.  will  be  required,  so  that, 
at  the  reduced  speed  of  7J  miles  per  hour,  the  horse- 
power becomes  30  X  7-5  =  225. 

For  the  same  duty  by  the  endless  rope  system,  the 
delivery  of  coal  to  the  pit  bottom  being  600  tons  in  10 
hours,  or  60  tons  per  hour,  i.e.,  1  ton  per  minute,  the 
power  calculation  is  as  follows  :~ 


Speed  of  haulage  in  miles  per  hour 
Length  of  road,   1  mile 
Gradient  against  the  load 
Coal  delivered  per  hour 
Coal  delivered  per  minute 


2. 

1,760  yds. 
4  in.  per  yd. 
60  tons. 
1  ton. 


102  ELECTRICAL  MINING  INSTALLATIONS 

Weignt  of  coal  per   tub  -  .          .          .10  cwts. 
Number  of  tubs  delivered  per  minute  to 

pit  bottom     .          .          .          .          .2. 
Yards  travelled  per  minute  by  rope  on 

two  miles  per  hour          .          .          .      58-6. 
Distance  of  tubs  apart  on  rope  .     29-3  yds. 

Number  of  full  tubs  on  rope      .          .      60. 
Number  of  empty  tubs  on  rope  .      60. 

With  the  endless  rope  system  the  full  and  empty 
tubs  balance  each  other,  and  it  is  therefore  only 
necessary  to  deal  with  the  actual  weight  of  the  coal. 

On  reference  to  the  horse-power  given  in  the  end- 
less rope  power  Table  II,  it  will  be  seen  that  for  an 
output  of  2,250  Ib.  per  minute,  which  is  the  nearest 
in  the  table  to  2,240  Ib.,  or  1  ton,  on  a  road  1,000  yds. 
long,  with  a  gradient  of  4  in.  to  the  yard  against  the 
load,  we  shall  require  34  H.P. 

With  the  endless  rope  system  the  horse-power  is 
increased  in  accordance  with  the  length  of  -the  road, 
Therefore,  the  horse-power  for  a  road  1  mile  long 
becomes  34  x  H££  =  6°  H.P. 

In  addition  to  the  foregoing  types  of  haulage  gear, 
we  may  also  mention  small  portable  haulages,  for 
auxiliary  work,  such  as  hauling  material  from  the 
working  parts  to  i/he  main  haulage  rope.  Such  sets 
are  usually  quite  small,  and  often  the  power  required 
does  not  exceed  5  H.P.  These  haulage  gears  may  be 
similar  to  any  one  of  the  three  already  described, 
though  they  usually  take  the  form  of  main  haulage 
with  one  rope,  but  in  any  case  the  use  of  such  auxiliary 
plants  makes  for  economy  in  working,  as  it  dispenses 
with  ponies  and  only  one  or  two  boys  will  be  found 
necessary  for  coupling  up  the  tubs,  etc.,  so  that  con- 
siderable saving  in  working  expenses  may  be  effected. 

There  is  also  another  system  of  haulage  used  to  a 
small  extent  in  colliery  work,  viz.,  haulage  by  electric 
locomotives,  but  up  to  the  present  this  method  has 
not  found  much  favour  in  this  country.  The  endless 
rope  haulage  system  is  preferred,  and  it  must  be  ad- 
mitted that  it  has  several  advantages  over  the  loco- 


ELECTRIC  HAULAGE  103 

motive,  notably  as  regards  efficiency  and  general 
convenience. 

Dealing  first  with  the  question  of  efficiency,  it  is 
obvious  that  a  great  deal  of  power  is  necessarily  wasted 
in  moving  the  locomotive,  which  must  itself  be  heavy 
to  give  sufficient  adhesion.  Again,  when  locomotives 
are  employed  more  room  is  required  in  the  roads, 
despite  the  fact  that  designers  have  made  mine- 
locomotives  as  compact  as  possible,  and  the  increased 
space  required  is  usually  sufficient,  in  itself,  to  prohibit 
the  adoption  of  this  form  of  traction  or  haulage. 

There  are,  however,  a  few  instances  where  loco- 
motives can  be,  and  are,  used  with  advantage,  and 
these  are  all  operated  on  the  low  or  medium  tension 
continuous-current  system.  The  Home  Office  rules 
are  very  strict  in  regard  to  the  use  of  locomotives,  as 
the  following  extract  will  show. 

"  Electric  haulage  by  locomotives  on  the  trolley 
wire  system,  is  not  permissible  in  any  place  or  part  of 
a  mine  where  General  Rule  No.  8  of  the  Coal  Mines 
Regulation  Act,  1887,  applies.  On  this  system  no 
pressure  exceeding  the  limits  of  medium  pressure  may 
be  employed. 

"  In  underground  roads,  the  trolley  wires  must  be 
placed  so  that  they  are  at  least  7  ft.  above  the  level  of 
the  road  or  track,  or  elsewhere,  if  sufficiently  guarded, 
or  the  pressure  must  be  cut  off  from  the  wires,  during 
such  hours  as  the  roads  are  used  for  travelling  on  foot, 
in  places  where  trolley  wires  are  fixed.  The  hours 
during  which  travelling  on  foot  is  permitted  shall  be 
clearly  indicated  by  notices,  and  signals,  placed  in  a 
conspicuous  position  at  the  ends  of  the  roads.  At 
other  times  no  one  other  than  a  duly  authorized  person 
shall  be  permitted  to  travel  on  foot  along  the  road. 

"  On  this  system  either  insulated  returns  or  unin- 
sulated metallic  returns  of  low  resistance  may  be 
employed. 

"  In  order  to  prevent  any  other  part  of  the  system 
being  earthed  (except  when  the  concentric  system 


104  ELECTRICAL  MINING  INSTALLATIONS 

with  earthed  outer  conductor  is  used)  the  current 
supplied  for  use  on  the  trolley  wires  with  an  uninsu- 
lated return  shall  be  generated  by  a  separate  machine, 
and  shall  not  be  taken  from,  or  be  in  connexion  with, 
electric  lines  otherwise  completely  insulated  from 
earth. 

"If  storage  battery  locomotives  are  used  in  any 
place  or  part  of  a  mine  where  General  Rule  No.  8  of 
the  Coal  Mines  Regulation  Act,  1887,  applies,  the 
rules  applying  to  motors  in  such  places  shall  be  also 
deemed  to  apply  to  the  boxes  containing  the  cells." 

Dismissing  storage  battery  systems  for  the  present 
as  impracticable,  it  may  be  stated  that  the  earthed 
return  is  the  only  system  commercially  possible.  This 
means  that  one  live  bare  trolley  wire  is  used,  and  the 
current  returned  through  the  track,  which  is,  of  course, 
in  connexion  with  earth.  The  alternative  to  this 
system  would  be  two  trolley  wires,  and  two  trolleys, 
but  the  complication  would  put  such  a  system  out  of 
court  altogether  for  mining  work. 

As  the  earthed  return  is  objectionable  the  Home 
Office  have  stipulated  that  a  separate  electric  genera- 
tor shall  be  used  to  supply  energy  to  locomotives,  so 
that  the  earthed  return  does  not  represent  an  earth  on 
the  electrical  system  in  general  use  throughout  the 
mine.  This  usually  means  the  adoption  of  an  inde- 
pendent motor-generator  for  supplying  the  locomotive 
section,  which  may  be  placed  down  the  shaft  if  possible, 
or  perhaps  on  the  surface,  in  which  case  another  set  of 
cables  will  be  required  down  the  shaft  to  supply  the 
locomotive  circuit. 

Taking  everything  into  consideration  it  will  be 
admitted  that  there  are  several  obstacles  to  overcome 
before  haulage  by  electric  locomotives  underground  is 
possible,  and  it  is  perhaps  not  surprising  that  little 
headway  has  been  made  in  connexion  with  this 
system. 

The  electrical  equipment  of  a  locomotive  would 
usually  consist  of  two  continuous-current  motors,  each 


ELECTRIC  HAULAGE  16S 

driving  one  axle  through  single  reduction  spur  gear- 
ing, and  controlled  by  means  of  a  series  parallel  con- 
troller. With  the  small  amount  of  room  available, 
and  the  narrow  gauge  often  adopted,  it  has  been 
rather  a  problem  to  design  an  electric  motor  to  fulfil 
the  required  conditions. 

The  series-parallel  system  of  control,  as  its  name 
implies,  starts  up  the  two  motors  in  series,  with  resist- 
ance in  circuit,  and,  as  the  controller  handle  is  moved 
round,  the  resistance  is  gradually  cut  out,  leaving  the 
motors  running  in  series  at  approximately  half  speed. 
On  further  moving  the  controller  handle  the  motors 
are  coupled  in  parallel  with  the  resistance  again  in 
circuit ;  this  is  gradually  cut  out,  step  by  step,  until 
both  motors  are  running  in  simple  parallel  across  the 
line.  All  these  movements  are  carried  out  by  one 
hand  wheel  on  the  controller,  but  another  handle  is 
usually  provided  for  reversing. 

In  the  case  of  small  locomotives  a  single  series- 
wound  motor  may  be  used  with  resistance  control 
similar  to  that  adopted  for  ordinary  haulage  gears. 

The  trolley  wire  is  usually  suspended  by  means  of 
insulated  hangers  carrying  an  ear,  into  which  the  wire 
is  soldered.  The  current  collecting  device  fitted  to 
the  locomotive  is  known  as  the  trolley,  and  may  be 
of  the  ordinary  tramway  pattern,  which,  however, 
requires  reversing  every  time  the  locomotive  changes 
its  direction  of  running,  or,  preferably,  the  bow  type, 
having  a  roller  pressing  upwards  against  the  trolley 
wire,  as  this  form  enables  the  driver  to  run  in  either 
direction  without  giving  any  attention  to  the  trolley. 

Some  electric  locomotives  are  also  fitted  with  a  reel 
of  insulated  wire  to  allow  of  their  working  in  a  posi- 
tion beyond  the  limits  of  the  trolley  wire  system. 

Electric  locomotives  are,  of  course,  fitted  with  the 
usual  hand  brakes,  and,  in  addition,  it  is  usual  to 
arrange  the  controller  with  a  rheostatic  brake,  which 
is  merely  an  arrangement  of  connexions,  converting 
the  motors  into  generators  and  absorbing  the  energy 


106  ELECTRICAL  MINING  INSTALLATIONS 

by  means  of  resistances,  when  stopping  or  descending 
an  incline. 

One  point  must  not  be  lost  sight  of  when  dealing 
with  this  system  of  haulage,  viz.,  that  the  locomotive 
must  be  heavy  enough  to  give  the  necessary  adhesion 
to  the  rails,  the  weight  being  a  function  of  the  draw- 
bar pull  required. 

Generally  speaking,  heavier  rails  are  necessary  for 
locomotive  traction  than  with  rope  haulages,  and, 
further,  the  track  must  be  laid  with  greater  care,  and 
must  be  bonded  electrically  in  order  to  preserve  a 
continuous  electrical  circuit  for  the  return  current. 


CHAPTER    VII 
ELECTRIC  PUMPING 

THE  driving  of  a  pumping  plant  by  electrical  energy 
is  one  of  the  most  important,  if  not  the  most  important, 
detail  in  an  electrically  equipped  mine.  With  pump- 
ing plant  one  of  the  first  essentials  is  reliability  as  in 
many  cases  a  stoppage,  even  for  a  short  time,  might 
involve  serious  loss  and  damage.  The  type  of  pump 
used  for  mining  purposes  during  the  last  part  of  the 
nineteenth  century  was  that  known  as  the  "  Cornish  " 
pump,  consisting  of  an  old-fashioned  beam  engine, 
at  the  top  of  the  shaft,  running  perhaps  as  slowly  as 
four  strokes  per  minute,  and  operating  a  pump  cylin- 
der underground  through  the  medium  of  long  connect- 
ing rods.  Needless  to  say,  the  arrangement  was 
most  uneconomical,  but  mining  engineers  had  to  be 
content  with  this  plant  or  face  the  problem  of  using 
steam  in  the  mine.  Under  the  circumstances  it  is 
not  surprising  that  electrically  driven  pumps  made 
so  much  headway,  and  it  is  now  generally  acknow- 
ledged that  electricity  is  far  superior  to  any  other 
power  for  this  particular  duty. 

Pumping  machinery  may  be  divided  into  two  main 
classes,  (a)  reciprocating  pumps  ;  either  of  the  ram  or 
piston  type,  (b)  rotary  pumps  ;  known  as  the  centri- 
fugal or.  turbine  pattern.  Both  types  are  used  for 
mining  work  and  both  are  suitable  for  electric  driving. 
Dealing  first  with  reciprocating  pumps  we  find  that 
these  are  available  in  several  forms,  according  to  the 
purpose  for  which  they  are  required,  and  the  local 
conditions  with  which  they  have  to  comply. 


108  ELECTRICAL  MINING  INSTALLATIONS 

The  piston  pump  may  be  dismissed  without 
further  comment  as  it  is  now  very  seldom  used  for 
mining  work,  and  the  type  known  as  the  "ram  "  is 
that  always  adopted  when  a  reciprocating  pump  is 
installed. 

The  ram  pump  is  single  acting  and  has  rams  of  cast 
iron,  gunmetal,  or  other  special  material,  working 
through  glands.  Such  pumps  are  usually  made  with 
three  cylinders  or  barrels  side-by-side,  and  the  rams 
driven  by  a  three-throw  crankshaft  having  cranks  at  an 
angle  of  120°.  This  form  of  construction  gives  a 
practically  continuous  flow  of  water,  and  has  no 
dead  centres  as  is  the  case  with  a  two-cylinder,  two- 
throw  pump,  which  is  occasionally  used  in  small 
capacities. 

The  ram  pump  may  be  of  the  vertical,  or  of  the 
horizontal  pattern,  the  type  selected  for  any  particu- 
lar purpose  depending,  among  other  things,  upon  the 
amount  of  head  room  and  floor  space  available. 

The  speed  of  the  ram  pump  is  necessarily  low  and 
some  form  of  speed  reduction  gear  must  be  introduced 
when  driving  from  an  electric  motor.  For  instance, 
a  three- throw  pump  having  rams,  8  in.  in  diameter  x 
12  in.  stroke,  would  run  at  about  40  r.p.m.,  thereby 
delivering  about  250  gallons  of  water  per  minute,  and, 
assuming  a  head  of  about  600  feet,  a  motor  of  65 
B.H.P.  would  probably  be  required. 

A  suitable  speed  for  a  motor  of  this  size  is  750  r.p.m., 
so  that  it  would  be  necessary  to  have  a  speed  reduction 
of  750  :  40,  or  18-75  :  1. 

If  gearing  only  be  employed  this  must  be  of  the 
double  reduction  type,  and  the  usual  practice  is  to  fit 
a  steel  pinion  on  the  motor  engaging  with  a  cast-iron 
machine-cut  spur  wheel  on  the  first  motion  shaft. 
The  second  motion  gearing  will  usually  consist  of 
cast-iron  pinion  and  gear  wheel,  having  machine- 
moulded  teeth.  Where  floor  space  is  no  object  a  rope 
drive  is  sometimes  employed  in  place  of  the  first 
reduction  gear. 


ELECTRIC  PUMPING 


109 


The  turbine  or  centrifugal  pump  is  so  simple  in 
principle  that  little  description  is  required,  but 
it  may  be  stated  that  this  class  of  pump  is  at  the  same 


time  most  difficult  from  the  designer's  point  of  view, 
when  any  particular  set  of  conditions  has  to  be  ful- 
filled to  the  best  advantage,  and  at  the  highest  possi- 


110  ELECTRICAL  MINING  INSTALLATIONS 

ble  efficiency.  The  plain  centrifugal  pump,  with 
single  impeller,  is  only  suited  for  small  delivery  heads. 
In  cases  where  water  is  to  be  delivered  against  greater 
heads,  the  turbine  construction  must  be  adopted. 

Fig.  26  shows  a  section  through  a  multi-stage 
turbine  pump,  designed  by  Messrs.  Jens  Orten  Boving, 
and  constructed  by  Messrs.  Willans  &  Robinson,  of 
Rugby.  These  pumps  may  run  at  almost  any  speed 
according  to  the  quantity  of  water  and  the  head,  a 
speed  of  3,000  r.p.m.  being  not  uncommon  although 
about  1,500  r.p.m.  is  perhaps  more  usual.  It  will  be 
seen  that  turbine  pumps  are  eminently  suited  for 
electric  driving,  in  fact  it  is  probable  that  this  type 
of  pump  would  never  have  been  developed  at  all  had 
it  not  been  for  electric  driving. 

The  motors  and  pumps  are  direct-coupled,  either 
through  a  rigid  or,  more  usually,  a  flexible  coupling, 
and  the  motor,  together  with  the  pump,  are  mounted 
on  a  common  cast-iron  bedplate,  thereby  making  a 
single  rigid  unit  which  may  be  easily  transferred  and 
erected  where  required. 

Selection  of  the  best  type  of  pump  for  any  particu- 
lar duty  is  a  very  important  consideration,  and  great 
care  must  be  exercised.  It  may  be  well  to  consider 
here  the  limitations  and  relative  advantages  of  the 
two  types  of  pumps  above  referred  to. 

The  ram  pump  may  be  designed  for  practically  any 
duty  required  in  practice,  but  it  must  be  remembered 
that  the  cost  will  be  more  than  that  of  a  centrifugal 
or  turbine  pump  where  the  conditions  are  such  as  to 
permit  the  latter  being  used,  and  this  difference  in 
cost  is  all  the  more  marked  when  a  pump  is  required 
to  deal  with  large  quantities  of  water  at  a  relatively 
low  head.  Again,  a  ram  pump  requires  more  room, 
but,  on  the  other  hand,  is  more  easily  maintained,  and 
does  not  require  any  special  technical  knowledge  on 
the  part  of  those  responsible  for  its  behaviour.  In 
the  event  of  a  fault  occurring  it  can  be  remedied  locally 
without  loss  of  time  and  inconvenience. 


ELECTRIC  PUMPING  111 

The  turbine  pump,  however,  is  different,  and  it  is 
necessary  that  pumping  sets  of  this  character  be  in- 
stalled with  great  care,  as  any  possible  alteration  in 
the  conditions  for  which  they  were  originally  designed 
may  render  the  whole  plant  useless.  In  this  con- 
nexion it  must  be  remembered  that  a  centrifugal  or 
turbine  pump,  designed  for  any  particular  head,  will 
not  deliver  above  that  head  unless  the  speed  be  in- 
creased, and,  while  with  continuous  current  motors  it 
is  possible  to  increase  the  speed  by  means  of  shunt 
resistance,  it  would  be  quite  impossible  to  effect  this 
alteration  with  an  alternating  current  motor.  Further, 
any  diminution  in  the  head  may  increase  the  quan- 
tity of  water  far  in  excess  of  that  for  which  the  pump 
is  designed,  and  this  increase  is  often  out  of  all  pro- 
portion to  the  reduction  in  head,  the  result  being  that 
the  motor  is  seriously  overloaded  and  may  be  burnt 
out. 

There  are,  however,  turbine  pumps  on  the  market  so 
designed  that  the  increase  in  quantity  of  water  is  more 
or  less  proportioned  to  the  reduction  in  head,  and  with 
such  pumps  there  would  not  be  this  possibility  of 
trouble  due  to  the  overloading  of  the  motor.  The 
characteristic  performance  of  such  a  pump  is  shown  in 
Fig.  27. 

A  turbine  pump  is  unsuitable  for  dealing  with  a 
small  quantity  of  water  at  a  relatively  large  head, 
and  the  best  conditions  are  realized  when  the  quan- 
tity of  water,  in  gallons  per  minute,  is  equal  to  the 
head,  in  feet.  If  the  head,  in  feet,  greatly  exceeds 
the  gallons  per  minute,  the  efficiency  of  the  turbine 
pump  is  low,  and  the  cost,  compared  with  a  ram  pump, 
less  favourable,  so  that  under  these  conditions  it  may 
be  better  to  adopt  a  ram  pump  for  such  duty. 

Electric  motors  for  driving  ram  pumps  will  usually 
be  of  the  protected,  or  totally  enclosed  type.  On 
alternating  current  systems  it  is  usual  to  adopt  wound 
rotor  machines  with  slip  rings  for  ram  pumps,  where 
the  torque  at  starting  maybe  considerable,  the  machine 


112     ELECTRICAL  MINING  INSTALLATIONS 


being  used  in  connexion  with  a  rotor  starting  resist- 
ance in  the  ordinary  way. 

If  plants  are  required  to  run  continuously  for  long 
periods,  it  is  customary  to  fit  the  motor  with  a  short- 


d'H'd 


7 


L 


o 

§ 


o 
O 


O 
O 


circuiting  and  brush  lifting  device,  in  order  to  save 
wear  and  tear  on  the  slip  rings  and  brushes.  With 
this  device  the  machine  is  started  up  by  means  of  a 
rotor  starting  resistance,  and,  when  the  set  is  running 


ELECTRIC  PUMPING 


113 


at  full  speed  the  rotor  windings  are  short  circuited 
by  means  of  a  lever  or  knob  at  the  end  of  the  shaft,  and 
the  brushes  raised  off  the  slip  rings.  This  not  only 
reduces  wear  and  tear,  but,  if  the  starting  resistance 
happens  to  be  placed  some  distance  from  the  motor, 
there  may  also  be  a  gain  in  efficiency,  and  less  slip 
by  reason  of  the  elimination  of  losses  in  the  rotor  con- 
necting cables.  It  must  not  be  forgotten,  however, 
after  shutting  down  such  a  motor,  to  re-set  the  short 
circuiting  and  brush -lifting  device,  otherwise  there 
may  be  trouble  when  it  is  required  to  start  again. 

For   alternating-current   motors    driving    turbine 
pumps  it  is  usual  to  adopt  the  short-circuited  rotor 


Sfator 
Windings 


FIG.  28.     AUTO    TRANSFORMER    STARTER    DIAGRAM. 

form  of  construction,  because  this  is  more  suitable 
for  high  speed  working,  and  the  cost  is  also  less  than 
that  of  wound  rotor  machines  with  slip  rings.  It  is 
possible  to  adopt  short-circuited  rotor  machines  in 
connexion  with  turbine  pumps  because  the  starting 
torque  is  low,  and  the  machines  start  light,  the  torque 
increasing  as  a  function  of  the  speed. 

The  torque  during  the  starting  period,  with  stop 
valve  closed,  corresponds  approximately  to  one-third 


114   ELECTRICAL  MINING  INSTALLATIONS 

full  load  torque  ;  then,  if  the  valve  is  opened,  the 
torque  will  gradually  rise  to  the  normal  full  load 
running  torque. 

This  method  of  starting  lends  itself  admirably  to 
the  use  of  induction  motors  having  short-circuited 
rotors,  used  in  conjunction  with  an  auto-transformer 
starter  or  a  star-mesh  starter,  whilst  small  sets  can  be 
switched  directly  on  the  mains,  provided  the  current 
taken  is  not  sufficient  to  disturb  the  supply  system  to 
any  great  extent.  The  usual  arrangement  of  auto- 


tLine  jf  Line 

FIG.  29.     STAB  MESH  STARTER. 


Line 


starting  transformers  is  shown  in  Fig.  28,  and  of 
star-mesh  controllers  in  Fig.  29. 

A  good  deal  of  misunderstanding  obtains  in  regard 
to  the  starting  current  and  corresponding  torque  of 
three-phase  induction  motors  having  short-circuited 
rotors,  and  it  may  be  as  well  here  to  clear  up  some  of 
these  problems. 

In  order  to  understand  the  case  aright  it  is  necessary 
to  realize  that  a  motor  of  this  type  always  exerts  its 


ELECTRIC  PUMPING          .        115 

maximum  torque  at  starting,  according  to  the  elec- 
trical conditions  and  quite  independent  of  external 
load.  This  at  first  sight  may  appear  incorrect,  but 
when  once  it  is  realized  that  the  maximum  possible 
torque  is  utilized  for  accelerating  the  load,  and  the 
revolving  parts  of  the  motors,  it  will  be  seen  that  the 
matter  at  once  resolves  itself  into  a  question  of  the 
time  required  for  acceleration. 

If  the  motor  has  a  heavy  load  to  run  up  to  speed  the 
time  required  for  acceleration  will  be  greater  than  if 
the  motor  had  only  to  accelerate  its  own  mass,  but 
the  torque  developed  in  either  case  will  be  the  same, 
viz.,  the  maximum  possible,  depending  upon  the  motor 
and  the  electrical  conditions. 

The  whole  question  of  motor  torque  is  bound  up 
with  the  characteristics  of  the  particular  make  of 
motor  adopted,  but  in  any  case  it  may  be  taken  that 
the  maximum  torque  is  a  function  of  the  terminal 
voltage  and  varies  directly  as  the  square  of  the  latter. 

As  a  general  rule  it  may  be  stated  that  a  motor  can 
develop  twice  full  load  torque  with  normal  voltage, 
about  full  load  torque  with  70  per  cent,  of  normal 
voltage,  and  J-load  torque  with  50  per  cent,  of  normal 
voltage,  according  to  the  resistance  of  the  rotor 
windings. 

In  the  first  case  the  motor  would  be  switched 
directly  on  the  line,  and  the  current  taken  would  be 
in  the  order  of  four  times  the  normal  running  current, 
but  assuming  an  auto-transformer  is  used  in  the  other 
cases,  with  voltage  ratios  of  70  per  cent,  and  50  per 
cent.,  the  current  taken  from  the  line  will  be  approx- 
imately twice  full  load,  and  normal  full  load,  ninning 
current  respectively. 

Auto-transformers  are  usually  provided  with  a 
number  of  tappings,  any  set  of  which  may  be  utilized 
according  to  the  percentage  pressure  and  torque  re- 
quired to  suit  the  conditions  of  starting.  With  star- 
mesh  starters  the  percentage  voltage  is,  of  course, 
fixed,  and  is  given  by  the  expression  100  times  -y/3=57 


116  ELECTRICAL  MINING  INSTALLATIONS 

per  cent.,  so  that  the  machine  started  up  in  this  man- 
ner will  develop  a  little  more  than  half  -full  load  torque. 
It  must  be  remembered  that  if  star  -mesh  starters 
are  adopted  the  motors  must  be  provided  with  six 
terminals,  as  shown  in  Fig.  29. 

With  alternating  -current  motors  the  speed  is 
limited  to  a  certain  extent  by  the  frequency  of  the 
supply  system.  The  light  load  speeds  may  be  found 
from  the  formula  — 


When  F  is  the  frequency  in  cycles  per  second  and  P.P. 
the  number  of  pairs  of  poles  on  the  motor.  Theoretic- 
ally P.P.  may  be  any  whole  number,  but  there  is  a 
limit  to  the  number  of  pairs  of  poles  for  construc- 
tional reasons. 

Generally  speaking,  it  is  preferable  to  run  alternat- 
ing current  motors  at  as  high  a  speed  as  convenient, 
in  order  to  keep  down  expense,  and  at  the  same  time 
obtain  a  better  machine.  For  any  particular  horse- 
power required  it  must  be  remembered  that  the  slower 
the  speed  the  lower  will  be  the  efficiency  and  also  the 
power  factor. 

The  speed  given  by  the  above  formula  is  that  at 
which  the  motor  will  run  without  load.  The  full  load 
speed  will  be  slightly  less  than  this,  the  difference 
between  the  speeds  at  light  load  and  full  load  being 
known  technically  as  "  slip."  This  "  slip  "  is  usually 
expressed  as  a  percentage,  and  its  value  may  be 
anything  up  to  8  per  cent,  for  small  motors  of  1 
B.H.P.,  to  5  per  cent,  in  motors  of  10  B.H.P.  With 
still  larger  machines  the  slip  may  be  only  3  per  cent. 
for,  say,  50-100  H.P.  and  even  lower  in  the  case  of 
very  large  powers. 

The  speed  of  alternating  current  motors  is  of 
course  independent  of  the  voltage  except  in  the  special 
case  referred  to  in  detail  in  Chapter  IX.  When  con- 
tinuous-current motors  are  employed  the  machines 
can  be  designed  for  any  speed  desired.  Then  ma* 


ELECTRIC  PUMPING  117 

chines  are  usually  shunt  Wound  for  both  plunger  and 
also  turbine  pumps,  but  may  be  occasionally  com- 
pound-wound in  the  former  case,  where  it  is  necessary 
to  start  up  against  a  heavy  load  such  as  a  long  column 
of  water  in  the  delivery  pipe. 

The  horse-power  required  to  drive  a  pump  of  any 
description  is  given  by  the  formula — 

HP=  WxH 
33,000 

Where  W  equals  the  weight  of  water  raised  per 
minute,  and  H  the  total  head  in  feet. 

This  expression  gives  the  theoretical  or  water  horse- 
power and  the  result  must  be  increased  to  allow  for 
the  efficiency  of  the  pump.  For  instance,  if  the  pump 
efficiency  is  70  per  cent.,  the  water  horse-power  must 
be  increased  in  the  proportion  of  70  :  100. 

In  dealing  with  all  pumping  problems  we  constantly 
meet  the  expression  "  total  head  "  which  includes  : — 

(a)  The  head   due   to   suction   (i.e.,   height  from 

suction  level  to  pump). 

(b)  The  head  due  to  delivery  (i.e.,  height  from 
pump  to  delivery  level). 

(c)  The  head  due  to  pipe  friction. 

All  heights  must  of  course  be  reckoned  vertically. 
The  head  due  to  suction  is  limited,  and,  with  the 
barometer  at  30  in.  cannot  be  more  than  33  ft.  theo- 
retically. In  practice  it  is  necessarily  less,  because 
we  cannot  produce  anything  like  a  perfect  vacuum 
with  ordinary  pumping  machinery,  and  with  pipe 
lines  and  joints  as  usually  constructed.  It  will  be 
found  that  24  ft.  suction,  including  the  head  due  to 
friction  in  the  suction  pipe,  is  all  that  can  be  expected, 
and  it  may  often  be  found  impossible  to  obtain  as 
much  as  24  ft.  suction. 

With  short  suction  and  delivery  pipes  the  increase 
in  head  due  to  friction  is  negligible,  and  may  be  dis- 
regarded, but  with  long  pipe  lines  it  becomes  an 
important  factor  and  has  to  be  reckoned  with.  The 
equivalent  increase  in  head  may  be  calculated  from 


118  ELECTRICAL  MINING  INSTALLATIONS 


well  known  formulae  when  the  velocity  of  the  water 
in  the  pipes  and  their  internal  diameter  are  known. 
This  calculation,  however,  is  rather  laborious,  and 
the  following  table  has  been  prepared  in  order  that 
the  desired  result  may  be  obtained  more  easily.  In 
using  this  table  we  only  require  to  know  the  quantity 
of  water  delivered,  in  gallons  per  hour,  together  with 
the  internal  diameter  of  the  pipes  proposed.  From 
this  table  it  will  also  be  possible  to  determine  the 

APPROX.  FRICTION  IN  FEET  HEAD  PER  YARD  OF  PIPE. 


Galls, 
per 
hour. 

DIAMETER  OP  PIPE  IN  INCHES. 

2 

3 

4 

5 

6 

7 

8 

9 

10 

12 

600 

•0133 

•0017 

1,200 

•0516  -0070 

•0016 

— 

— 

— 

— 

— 

— 

— 

1,800 

•1158-0158 

•0038 

•0012 

— 

— 

— 

— 

— 

— 

2,400 

•2060-0277 

•0066 

•0021 

— 

— 

— 

— 

— 

— 

3,000 

— 

-0426 

•0105 

•0035 

•0013 

— 

— 







3,600 

— 

•0609 

-0145 

•0049 

•0020 

— 

— 

— 





4,800 

— 

•1089 

•0259 

•0084 

•0035 

•0016 

— 

— 

— 

— 

6,000 

— 

•1695 

•0405 

•0134 

•0056 

•0026 

•0013 

— 

— 

— 

7,500 

— 

-2650 

•0625 

•0215 

•0084 

•0039 

•0019 

•0011 

— 

— 

9,000 

— 

— 

•0905 

•0299 

•0129 

•0055 

•0029 

•0016 

•0010 

— 

10,500 

— 

— 

•1260 

•0450 

•0165 

•0078 

•0039 

•0022 

•0013 

— 

12,000 

— 

— 

•1650 

•0529 

•0216 

•0099 

•0055 

•0029 

•0016 

— 

15,000 

— 

— 

•2500 

•0835 

•0344 

•0155 

•0079 

•0045 

•0027 

•0010 

18,000 

— 

— 

— 

•1194 

•0486 

•0230 

•0116 

•0064 

•0039 

•0015 

21,000 

— 

— 

— 

•1622 

•0650 

•0310 

•0156 

•0085 

•0055 

•0021 

24,000 

— 

— 

— 

•2109 

•0856 

•0395 

•0204 

•0115 

•0068 

•0029 

27,000 

— 

— 

— 

•2269 

•1075 

•0496 

•0256 

•0144 

•0085 

•0034 

30,000 

— 

— 

— 

— 

•1333 

-0622 

•0314 

•0174 

•0105 

-0042 

36,000 

— 

— 

— 

— 

•1915 

•0892 

-0455 

•0251 

•0148 

•0065 

42,000 

— 

— 

— 

— 

•2598 

•1210 

•0616 

•0345 

•0204 

•0084 

48,000 

— 

— 

— 

— 

— 

•1569 

•0814 

•0446 

•0266 

•0116 

54,000 

— 

— 

— 

— 

— 

•1985 

•1019 

•0564 

•0335 

•0136 

60,000 

— 

— 

— 

— 

— 

•2460 

•1266 

•0710 

•0426 

•0165 

75,000 

— 

— 

— 

— 

— 

— 

•1959 

•1110 

•0655 

•0265 

90,000 

— 

— 

— 

— 

— 

— 

•2836 

•1560 

•1055 

•0377 

105,000 

— 

— 

— 

— 

— 

— 

— 

•2150 

•1353 

•0550 

120,000 

— 

— 

— 

— 

— 

— 

— 

•2780 

•1666 

•0664 

150,000 

~~ 

~~~ 

— 

— 

— 

— 

—  2 

•2592 

•1043 

ELECTRIC  PUMPING  119 

best  size  of  pipe  to  deal  with  any  given  quantity  of 
water.  In  addition  to  the  increase  of  head  by  reason 
of  pipe  friction,  it  must  not  be  forgotten  that  bends, 
change  of  direction,  or  change  in  the  size  of  pipe, 
may  occasion  some  loss  which  must  be  allowed  for. 

Another  class  of  pump  known  as  a  "  sinking  pump  " 
is  used  when  it  is  required  to  unwater  a  mine  that 
has  become  flooded.  This  sinking  pump  is  not 
fixed  but  is  suspended  from  chains  in  the  shaft,  and 
is  lowered  a  few  feet  at  a  time,  as  the  water  is  pumped 
out  of  the  mine. 

A  sinking  pump  may  be  of  the  plunger  or  the 
turbine  type. 

When  a  turbine  type  of  sinking  pump  is  employed 
this  is  always  of  the  vertical  shaft  pattern,  the  motor 
being  direct-coupled  above  the  pump,  through  a 
flexible  coupling.  This  form  of  coupling  is  absolutely 
necessary  with  a  vertical  shaft  pump  and  motor,  in 
order  to  ensure  that  the  weights  of  the  parts  are 
properly  taken  by  their  respective  bearings.  The 
pump  bearings  must  be  designed  to  take  not  only  the 
weight  of  the  impeller,  but  also  any  thrust  that  may 
arise,  while  the  motor  bearings  carry  the  weight  of 
the  armature  or  rotor  only. 

Motors  for  sinking  pumps  of  any  description  should 
preferably  be  of  the  totally-enclosed  type  or  should 
at  least  be  provided  with  an  efficient  shield  against 
water  and  dirt  dropping  down  from  above. 

If  the  motors  are  continuous  current,  they  should 
be  shunt  or  compound  wound,  while  for  three-phase 
work  it  is  preferable  to  use  machines  with  per- 
manently short-circuited  rotors.  This  is  to  save 
the  necessity  of  bringing  an  extra  three-core  cable 
up  the  shaft  from  the  slip  rings  to  the  rotor  starting 
resistance. 

Great  care  must  be  taken,  in  laying  out  a  sinking 
pump  installation,  to  see  that  the  motor  and  pump 
are  well  up  to  the  duty  required  and  it  is  a  great 
mistake  to  cut  things  fine  for  this  class  of  work.  If 


120  ELECTRICAL  MINING  INSTALLATIONS 

there  is  a  considerable  run  of  cable  from  the  generating 
station  to  the  pump,  due  allowance  must  be  made 
for  the  pressure  drop  in  this  cable.  With  a  con- 
tinuous current  system  the  loss  in  pressure  may 
cause  the  motor  to  run  slow,  and  it  will  then  be  unable 
to  pump  the  required  quantity  of  water,  while  if  the 
pump  happens  to  be  of  the  turbine  type  it  may  be 
impossible  to  get  any  delivery  at  all  if  the  speed  of 
the  motor  is  much  less  than  that  for  which  the  pump 
is  designed. 

With  an  alternating  current  system,  the  loss  in 
pressure  will  seriously  affect  the  starting  torque 
(which  varies  as  the  square  of  the  pressure  at  the 
motor  terminals)  and  the  Author  has  known  of  cases 
where  great  trouble  was  experienced  at  starting  due 
to  this  cause. 

It  is  not  always  commercially  practicable  to  so 
increase  the  size  of  the  connecting  cable  as  to  limit 
the  pressure  drop  to  say  5  per  cent.,  but  it  is  always 
possible  to  calculate  the  actual  voltage  delivered  at 
the  motor  terminals  and  design  the  machine  for 
this  pressure.  This  is  a  point  that  should  have 
attention  in  all  cases  when  motors  are  placed  at  a 
great  distance  from  the  power  station,  especially 
if  continuous-current  motors  are  used  for  driving 
turbine' pumps,  as  these  are  very  sensitive  to  com- 
paratively small  variations  in  speed. 

It  must  not  be  forgotten  that  all  centrifugal  or 
turbine  pumps  require  priming,  that  is  to  say  the 
pump  casing  and  suction  pipe  must  be  flooded  with 
water  before  the  pump  will  act.  This  priming  may 
be  done  from  the  main  delivery  pipe  in  some  cases, 
or  the  pump  casing  may  be  filled  from  any  water 
supply  system,  a  special  charging  or  priming  cock 
being  provided  on  the  casing  for  this  purpose.  It 
is  needless  to  state  that  a  non-return  valve  must  be 
provided  at  the  foot  of  the  suction  pipe  to  retain  the 
water. 

The  installation  of  a  sinking  pump  for  unwatering 


ELECTRIC  PUMPING  121 

a  mine  is  an  expensive  matter,  especially  if  the  plant 
has  no  further  use  after  completing  the  duty  for 
which  it  was  purchased.  For  this  reason  some 
makers  now  design  plants  which  can  be  used  as 
permanent  pumps  at  the  bottom  of  the  shaft  after 
sinking  operations  are  completed.  As  already 
mentioned,  in  the  case  of  a  turbine  pump  it  is  only 
possible  to  secure  the  best  efficiency  when  the  plant 
is  working  under  the  exact  conditions  for  which  it  has 
been  designed,  and,  consequently,  any  great  altera- 
tion in  these  conditions  means  considerable  loss  in 
efficiency. 

Now  it  is  evident  that  in  a  sinking  pump  installa- 
tion the  conditions  vary  very  much,  inasmuch  as 
the  head  may  be  only  a  few  feet  when  commencing 
to  unwater  the  mine,  and  may  increase  to  several 
hundred  feet  at  the  finish  of  the  operation. 

The  pump  must  obviously  be  designed  for  the 
maximum  load,  which  only  occurs  when  the  plant 
is  pumping  from  the  very  bottom  of  the  pit.  With 
a  plunger  pump  the  motor  will  run  continuously  at 
full  speed,  and  the  horse-power  absorbed  will  adjust 
itself  more  or  less  to  the  work  done.  With  a  turbine 
pump  the  case  is  very  different,  and  it  is  necessary 
to  vary  the  speed  of  the  motor  in  order  that  the 
pump  shall  deliver  the  required  quantity  at  the  vari- 
ous heads,  or,  alternatively,  a  throttle  valve  must 
be  used  on  the  delivery  pipe  which  is  equal  to  an 
artificial  head.  Speed  regulation  is  impossible  with 
polyphase  motors  of  the  short-circuited  rotor  type, 
and  is  difficult  to  carry  out  or  is  inefficient  with  other 
types  of  motor.  Under  the  circumstances  we  usually 
regulate  by  the  throttle  valve  on  the  delivery  pipe. 
This  arrangement  is  also  inefficient  as  the  motor  is 
practically  working  at  full  load  when  the  pump  is 
delivering  at  a  few  feet  head.  For  very  large  instal- 
lations, where  efficiency  is  of  first  importance,  multi- 
stage turbine  pumps  may  be  used,  one  stage  only 
being  employed  say  for  the  first  50  ft.,  the  second- 


122  ELECTRICAL  MINING  INSTALLATIONS 

stage,  third  stage,  etc.,  being  added  as  the  pump 
gets  deeper  and  deeper  in  the  shaft.  This  plan  main- 
tains a  high  efficiency  throughout  the  complete 
operation  of  un watering  a  mine. 

A  sinking  pump  must  of  course  be  provided  with 
a  winch,  and  wire  rope,  or  chain,  for  supporting  the 
complete  plant  from  the  top  of  the  shaft.  The  con- 
necting cables  must  be  of  rubber  in  order  to  be  flexible, 
the  two  or  three  conductors  being  formed  into  one 
cable,  and  suitably  armoured  and  protected  from  cor- 
rosion. A  suitable  cable  drum  must  be  arranged 
for  at  the  top  of  the  shaft  to  pay  out  the  cable  as 
required. 

In  mining  work  it  is  sometimes  necessary  to  provide 
small  dip  pumps  and  portable  pumps  for  use  in  the 
workings.  These  are  often  built  up  on  a  four-wheel 
truck  to  facilitate  transport.  These  pumps  do  not 
call  for  special  comment.  They  may  be  of  the 
plunger  or  turbine  pattern,  driven  by  continuous 
current  or  polyphase  motors.  If  flexible  connecting 
cables  are  used  for  portable  pumps,  the  reader  is 
referred  to  the  remarks  in  Chapter  V  in  reference  to 
these  cables. 


CHAPTER    VIII 
ELECTRIC  COAL  CUTTING  AND  DRILLING 

ELECTRIC  Coal  Cutting  is  yet  another  example  of 
the  machine  displacing  hand  labour,  although  in  this 
case  the  mining  engineer  usually  regards  it  as  a 
device  for  not  only  cheapening  the  cost  of  getting 
coal,  but  also  enabling  him  to  obtain  a  greater  quan- 
tity from  a  given  working,  than  would  be  possible 
with  hand  labour.  Coal  cutters  therefore  really 
increase  the  capacity  of  a  mine  provided  the  haulage 
plants  are  capable  of  dealing  with  the  quantity 
required  and  the  winding  engines  are  designed  to 
bring  the  desired  amount  to  the  surface.  If  one 
or  other  of  these  agencies,  however,  is  not  sufficient 
for  its  work,  then  the  quantity  of  coal  brought  up 
must  depend  upon  the  slowest,  just  as  the  strength 
of  a  chain  is  that  of  its  weakest  link. 

In  actual  practice  it  is  found  that,  with  a  given 
working  face,  three  times  the  output  may  be  obtained 
if  coal-cutting  machines  are  employed  instead  of 
hand  labour. 

In  addition  to  increasing  the  capacity  of  the  mine, 
and  cheapening  its  working,  there  are  other  considera- 
tions in  favour  of  coal-cutting  machinery  which  will 
appeal  to  mining  engineers,  and  machine  working 
is  gradually  taking  the  place  of  hand  labour. 

Before  passing  to  the  electrical  aspect,  it  will  be 
as  well  to  mention  the  three  distinct  types  of  coal 
cutters  used,  according  to  local  requirements.  These 
are  respectively  known  as  "  The  Chain,"  "  The  Bar," 


124  ELECTRICAL  MINING  INSTALLATIONS 

and  the  "  Disc  Type,"  each  having  its  own  peculiar 
advantage  in  practice,  although  of  course  each 
particular  maker  has  special  claims  for  his  own 
pattern  of  machine. 

The  design  of  the  electric  motor  for  driving  coal 
cutters  has  presented  many  problems,  owing  to  the 
severe  conditions  under  which  it  is  required  to  work, 
and  to  the  necessity  for  restricting  its  dimensions 
to  a  degree  which  renders  it  difficult  to  obtain  the 
required  power. 

The  standard  electric  motor  will  not  do  at  all, 
and  the  coal-cutter  motor  (like  the  traction  motor) 
is  a  speciality,  designed  for  its  own  particular  purpose. 
It  goes  without  saying  that  the  machine  must  be  very 
well  built ;  the  shaft  must  be  extra  strong,  and  the 
magnet  coils  rigidly  fixed  to  the  pole  pieces,  as  the 
vibration  is  at  times  excessive.  The  motor  is  of 
course  totally  enclosed,  and  must  be  designed  to 
work  under  the  required  conditions,  without  an 
excessive  temperature  rise. 

The  starting  gear,  too,  must  be  of  strong  and 
robust  design,  liberally  rated  for  its  duty,  and  suitable 
for  rough  usage.  A  starter,  or  controller  of  the  drum 
type  is  best,  having  all  parts  enclosed  in  a  strong 
iron  case,  and  operated  by  an  external  handle  or 
hand  wheel. 

All  early  coal-cutter  motors  were  ofthe  continuous- 
current  type,  and,  as  may  be  expected,  trouble  was 
experienced  in  connexion  with  the  commutator  and 
brush  gear.  Many  coal-cutting  machines  have  been 
made  lately  with  three-phase  motors  having  per- 
manently short-circuited  rotors,  and  such  machines, 
When  a  three-phase  supply  is  available  are  distinctly 
advantageous.  The  starting  gear  for  these  three- 
phase  motors  is  of  the  simplest  possible  description, 
consisting  of  a  plain  triple-pole  switch  in  a  cast-iron 
case,  by  means  of  which  the  rotor  is  switched  direct 
on  to  the  circuit  without  the  use  of  any  resistances, 
the  current  taken  from  the  mains  under  these  con- 


ELECTRIC  COAL  CUTTING  AND  DRILLING  125 

ditions  being  equal  to  about  three  times  the  full  load 
running  current  of  the  motor.  This  mode  of  starting 
is  perhaps  more  suitable  for  the  bar  than  for  the 
disc  and  chain  types  of  cutter,  because  the  former 
starts  comparatively  light,  while  the  latter  require  a 
considerable  starting  torque.  In  a  three-phase  motor 
it  is  only  possible  to  obtain  a  high  starting  torque 
by  employing  a  high  resistance  rotor,  or,  what  comes 
to  the  same  thing,  a  resistance  in  the  rotor  circuit. 
This,  therefore,  means  that  for  disc  and  chain  ma- 
chines three-phase  motors  with  wound  rotors  must 
be  employed  in  conjunction  with  rotor  starting 
resistances. 

With  continuous  current  motors  some  coal-cutter 
makers  use  series-wound  machines  which  have  the 
advantage  of  a  high  starting  torque  and  good  overload 
capacity  which  are  very  useful  since  the  machine 
may  jam  or  meet  some  unexpected  obstruction  in 
cutting.  The  speed  of  the  series  motor  of  course 
falls  considerably  in  the  event  of  an  overload,  but 
this  is  perhaps  an  advantage,  because  the  total  horse- 
power used  is  consequently  less  than  if  the  speed 
remained  constant,  and  therefore  the  emergency 
demand  from  the  mains  is  also  less. 

Other  makers  recommend  shunt  motors,  which 
have  the  advantage  of  maintaining  an  approximately 
constant  speed,  even  when  running  quite  light,  under 
which  circumstances  the  series  motor  is  at  a  disad- 
vantage because  its  tendency  is  to  race. 

Compound-wound  motors  are  also  used,  and  it 
would  seem  that  they  are  the  most  suitable,  as  they 
possess  the  characteristics  of  both  shunt  and  series 
wound  machines. 

Motors  for  bar  coal-cutters  might  be  shunt  wound, 
or  have  a  light  series  winding,  whilst  those  for  disc 
and  chain  machines  would  be  compound-wound  with 
a  heavy  series  winding,  or  they  might  be  described 
as  series-wound  machines  with  a  light  additional  shunt 
winding,  sufficient  to  prevent  racing  on  light  load. 


126  ELECTRICAL  MINING  INSTALLATIONS 

As  the  electric  coal  cutter  is  essentially  a  portable 
machine,  it  cannot  be  permanently  connected  to 
the  supply  system.  This  means  that  a  length  of 
flexible  cable  is  required,  of  sufficient  length  to  follow 
the  machine  in  its  work,  one  end  being  attached  to 
the  machine  and  the  other  terminating  in  a  suitable 
connexion  box,  fixed,  and  permanently  connected 
to  the  main  supply  system,  at  the  nearest  point  to 
that  where  the  coal  cutter  is  at  work. 

In  accordance  with  Home  Office  regulations,  which 
state  that  motors  of  coal  cutters  and  other  portable 
machines  shall  not  be  used  at  a  pressure  higher  than 
medium  pressure,  it  follows  that  the  voltage  never 
exceeds  650.  The  trailing  cables  are  specified  to  be 
specially  flexible,  heavily  insulated,  and  protected 
with  either  galvanized  steel  rim  armouring,  extra 
stout  binding,  hose  pipe  or  other  effective  covering. 
It  is  also  imperative  that  these  trailing  cables  be 
examined  at  least  once  in  every  shift. 

At  the  point  where  the  connexion  box  is  fixed, 
it  is  also  necessary  to  provide  a  switch,  capable  of 
entirely  interrupting  the  supply  to  the  terminal  or 
connecting  box,  and  consequently,  to  the  coal-cutter 
motor. 

The  power  required  usually  varies  between  15 
H.P.  and  20  H.P.,  although  much  depends  upon  the 
make  and  type  of  machine  and  the  duty  put  upon  it. 

In  this  section  we  also  include  electric  drills  for 
colliery  work,  although  it  must  be  admitted  that  the 
field  for  this  type  of  drill  is  somewhat  limited.  The 
compressed  air  drill  has  been  used  almost  exclusively 
for  colliery  work  until  recently,  in  fact  even  now 
compressed  air  drills  are  still  desirable  for  certain 
operations. 

Electric  drills  for  colliery  work  are  of  two  distinct 
types,  viz.-,  "  rotary "  and  the  "  percussive,"  the 
latter  being  expressly  suitable  for  rock,  and  very 
hard  material,  where  a  rotary  drill  would  not  make 
any  impression, 


ELECTRIC  COAL  CUTTING  AND  DRILLING  127 

The  former  usually  consists  of  an  ordinary  motor, 
either  of  the  continuous  or  three-phase  alternating 
current  type,  driving  the  drill  through  the  medium 
of  gearing  or  a  flexible  shaft.  In  some  cases  the 
drilling  machine  is  mounted  on  a  four-wheeled  truck, 
but  in  other  situations  it  may  be  more  suitable  to 
attach  the  drill  to  a  rigid  stand,  fixed  in  position  by 
means  of  stays,  or  wedged  between  the  floor  and 
roof  of  the  workings,  the  power  being  communicated 
from  the  motor  by  means  of  a  flexible  shaft,  or  through 
universal  joints. 

These  machines  are  fitted  with  steel  drills  for  deal- 
ing with  soft  material,  and  diamond  drills  for  medium 
rocks.  When  hard  rocks  have  to  be  negotiated  the 
percussive  drill  is  employed.  This  type  is  recipro- 
cating and,  consequently,  ill  adapted  to  a  rotary 
motor  drive. 

In  one  form  electricity  is  made  to  act  electro- 
magnetically  upon  a  steel  plunger,  no  motor  being 
employed.  Two  coils  or  solenoids  are  provided  in 
the  drill  casing,  and  energized  alternately  by  current 
from  a  special  generator,  causing  the  steel  plunger 
to  oscillate  between  them,  with  a  slight  rotary  move- 
ment due  to  rifling  of  the  plunger.  This  drill  makes 
between  300  and  400  strokes  per  minute,  and  as 
several  such  machines  may  be  used  in  conjunction 
with  one  special  generator,  the  system  becomes 
extremely  flexible. 

Other  forms  of  percussive  drills  can  neither  be 
termed  electric  nor  compressed  air  drills,  but  are  essen- 
tially a  combination  of  the  two,  an  electrically 
driven  air  compressor  being  used  whilst  the  drill 
proper  is  of  a  simple  pneumatic  type. 

Despite  the  great  advances  made  in  connexion 
with  electric  coal  drills  in  the  past  few  years,  there 
are  those  who  still  favour  the  compressed  air  pattern, 
but  it  remains  that  in  most  of  these  cases  the  air 
compressors  are  electrically-driven  if  electrical  energy 
is  available,  for  economical  reasons. 


128   ELECTRICAL  MINING  INSTALLATIONS 

With  regard  to  the  supply  of  electricity  for  drills, 
there  is  not  much  to  be  said,  except  that  it  must 
be  of  low  or  medium  tension,  and  that  the  general 
rules  relating  to  the  use  of  portable  machines  in 
mines  must  be  observed. 

Flexible  cables  are  of  course  employed  to  a  great 
extent  and  the  same  rules  apply  as  mentioned  above 
in  connexion  with  electric  coal  cutters. 


CHAPTER   IX  ] 

ELECTRIC  VENTILATING 

WE  now  come  to  another  branch  of  mining  work  to 
which  electricity  has  been  applied  with  most  favour- 
able results,  namely,  ventilation. 

GENERAL  RULE  No.  1  of  the  Coal  Mines  Act,  re- 
quires that  an  adequate  amount  of  ventilation  shall 
be  constantly  produced  in  every  mine,  to  dilute,  and 
render  harmless,  noxious  gases,  to  such  an  extent 
that  the  working  places  of  the  shafts,  lures,  stables 
and  workings  of  the  mine,  and  the  travelling  roads 
to  and  from  these  working  places,  shall  be  in  a  fit 
state  for  working  and  passing  therein. 

In  earlier  days  it  was  customary  to  obtain  the 
necessary  ventilation  by  means  of  a  furnace  placed 
at  the  greatest  possible  depth  adjacent  to  the  upcast 
shaft.  This  method  worked  well  when  the  workings 
were  short,  and  consequently  offered  small  resistance 
to  the  passage  of  the  gases  ;  but  in  mines  having  long 
air  courses,  with  a  correspondingly  high  resistance, 
the  pressure  obtained  by  means  of  the  furnace  is 
insufficient  to  induce  the  necessary  change  of  air. 

In  these  cases  mechanical  ventilation  must  be 
employed,  and  the  first  step  was  to  instal  large  fans, 
usually  direct  coupled  to  steam  engines,  and  running 
at  a  slow  speed.  These,  it  must  be  admitted,  were 
reliable,  but  very  bulky  and  inefficient,  so  that  it 
is  not  surprising  that  their  place  is  being  taken  by 
smaller,  high  speed,  electrically-driven  fans. 

The  fans  usually  adopted  are  of  the  centrifugal 


130   ELECTRICAL  MINING  INSTALLATIONS 

type,  which  has  now  been  brought  to  a  high  pitch 
of  perfection.  They  are  either  direct-coupled  to 
the  motor  shaft,  or  driven  by  means  of  belt  or  ropes. 
The  fan  consists  of  a  runner,  or  impeller,  enclosed 
in  a  spiral  casing  very  similar  to  that  of  a  centrifugal 
pump,  and,  if  the  motor  speed  is  suitable,  this  runner 
is  often  mounted  direct  on  the  motor  shaft,  the  motor 
itself  being  placed  close  up  against  the  spiral  casing. 
This  arrangement  has  the  advantage  of  being  cheap 
and  compact,  while  there  are  only  the  two  motor 
bearings  to  look  after  and  lubricate.  A  combination 
bedplate  is  arranged  to  carry  both  motor  and  fan 
casing. 

It  must  be  understood  that  the  diameter,  width, 
and  speed  of  the  fan,  are  determined  by  the  quantity 
of  air,  and  pressure  required  for  ventilating  any 
particular  mine.  The  electric  motor  driving  the  fan 
must  then  be  designed  to  suit  these  conditions.  In 
many  cases  it  happens  that  a  fan,  running  at  a  com- 
paratively slow  speed,  is  necessary  to  fulfil  certain 
conditions,  in  which  case  it  may  be  preferable  to 
instal  a  belt  or  rope  drive  from  a  high  speed  motor, 
instead  of  a  direct  drive  from  a  large,  and  conse- 
quently more  expensive  slow  speed  motor. 

We  need  not  concern  ourselves  here  with  the 
design,  speed,  or  diameter  of  fans  for  any  particular 
service,  all  of  which  details  may  safely  be  left  to  the 
fan  maker ;  but  it  will  be  useful  to  determine  the 
horse-power  required  to  drive  a  fan  dealing  with  a 
given  quantity  of  air  at  a  certain  pressure. 

Let  V  =  the  capacity  of  fan  in  cubic  feet  per  minute. 

Let  P  —  the  pressure,  usually  measured  in  inches 
(water  gauge). 

Then  the  theoretical  horse-power  will  be  given  by 
the  expression  H.P.  =  V  X  P  X  5-2  +  33,000. 

The  constant,  5-2,  is  the  weight  of  one  square  foot 
of  water,  one  inch  deep,  which  is  the  equivalent  of 
1  in.  (water  gauge).  The  actual  horse-power  required 
to  drive  the  fan  must,  of  course,  be  increased  to  cover 


ELECTRIC  VENTILATING  131 

the  loss  in  conversion  and  the  efficiency  of  a  well 
designed  fan  will  be  in  the  neighbourhood  of  70  per 
cent. 

If  continuous-current  motors  are  adopted  it  is 
usual  to  provide  shunt  or  compound-wound  machines, 
and  it  is  advisable  to  instal  a  shunt  regulating  resist- 
ance in  order  that  the  speed  may  be  adjusted  to  suit 
the  exact  conditions. 

When  three-phase  motors  are  employed,  these 
may  with  advantage  be  of  the  short-circuited  rotor 
pattern,  in  order  to  save  the  wear  and  tear  of  slip 
rings.  In  such  case  the  motors  would  start  up  light 
in  conjunction  with  an  auto-transformer  starter. 

In  installing  fans  one  point  must  not  be  lost  sight 
of,  namely,  the  requirements  of  General  Rule  No.  3 
of  the  Act,  in  which  it  is  stated  that,  when  a  mechan- 
ical contrivance  for  ventilation  is  introduced  into 
any  mine,  it  shall  be  in  such  a  position  and  placed 
under  such  conditions,  as  will  tend  to  ensure  its 
being  uninjured  by  an  explosion. 

It  frequently  happens  in  connexion  with  mine 
fans,  that  some  method  of  reducing  the  capacity  is 
required  during  holidays  and  week  ends,  and  this 
may  be  easily  achieved  by  reducing  the  speed  of  the 
fan  and  motor.  With  continuous  current  motors 
the  necessary  speed  regulation  may  be  obtained  by 
means  of  resistance  in  series  with  the  armature,  or, 
if  a  more  economical  method  is  preferred,  by  regula- 
tion of  the  shunt  field  winding,  although  the  latter 
method  means  that  a  larger  and  consequently  more 
expensive  motor  will  be  required. 

With  three-phase  motors  having  wound  rotors 
and  slip  rings,  speed  regulation  may  be  obtained  by 
means  of  rotor  resistance,  which  is  analogous  to  the 
continuous-current  motor  regulated  by  resistance 
in  series  with  the  armature.  With  three-phase 
motors  having  short-circuited  rotors,  regulation  in 
speed  may  be  obtained  by  varying  the  pressure  at 
the  terminals.  This  may  be  effected  by  means  of  a 


132  ELECTRICAL  MINING  INSTALLATIONS 

controller  and  resistance,  or  by  an  auto-transformer 
or  choking  coil,  the  latter  method  having  the  advan- 
tage of  a  higher  efficiency. 

It  must  not  be  assumed  that  this  method  of  speed 
regulation  can  be  adopted  for  any  three-phase  motor 
of  the  short-circuited  rotor  type,  operating  on  any 
load.  We  have  already  seen  that  the  maximum 
torque  produced  by  any  three-phase  motor  varies  in 
proportion  to  the  square  of  the  voltage  ;  in  order 
therefore  to  secure  stable  speed  regulation  it  is 
necessary  that  the  torque  required  to  drive  should 
vary  in  proportion  to  some  higher  power  of  the  speed. 
In  the  case  of  the  fan,  the  torque  required  to  drive 
varies  as  the  cube  of  the  speed  ;  hence  the  necessary 
condition  is  fulfilled  for  this  particular  purpose, 
and  the  method  may  be  adopted  for  fan  driving. 

There  are  other  methods  of  speed  regulation  in 
connexion  with  three-phase  motors  sometimes  used 
when  these  machines  are  required  to  drive  fans. 
The  most  important  is  that  known  as  the  "  cascade 
system  "  and  is  analogous  to  the  well  known  series- 
parallel  control  for  continuous  current  machines. 
Two  similar  motors  are  used,  and  normally  run  in 
parallel  at  full  speed.  When  connected  in  cascade, 
the  rotor  windings  of  one  motor  must  be  connected 
to  the  starter  of  the  other. 

Under  these  conditions  the  first  motor  is  acting 
-  partly  as  a  motor  and  partly  as  a  transformer.  One 
half  of  the  energy  received  from  the  line  is  converted 
into  mechanical  energy  by  the  first  motor,  which 
runs  at  half  speed,  and  the  other  half  is  transmitted 
electrically  to  the  second  motor,  at  half  the  frequency 
of  the  initial  supply.  Both  motors  will  therefore 
run  at  half  speed,  and  develop  nearly  full  torque, 
the  energy  required  from  the  line  being  the  same 
as  would  be  necessary  to  drive  one  motor  alone. 

The  method  of  speed  control  is  very  efficient,  but 
there  is  no  intermediate  regulation  between  full  and 
half  speed.  But  in  cases  where  this  amount  of 


ELECTRIC  VENTILATING  133 

regulation  is  desirable,  and  the  complication  of  two 
motors  is  not  objected  to,  the  system  lends  itself 
admirably  to  the  purpose  of  driving  mine  fans. 

Another  method  of  varying  the  speed  of  three- 
phase  motors  is  by  changing  the  number  of  poles. 
This  also  is  an  efficient  method,  but  no  intermediate 
steps  between  full  speed  and  half  speed  can  be 
obtained. 

In  actual  practice  the  number  of  poles  is  changed 
by  paralleling  adjacent  poles.  For  instance,  assum- 
ing an  eight-pole  motor,  running  at  a  speed  of  750 
revolutions  per  minute  (synchronous  speed).  On 
a  50-cycle  circuit  the  poles  will  be  arranged  in  the 
order,  N.S.,  N.S.,  N.S.,  N.S.  By  paralleling  adjacent 
poles  we  now  obtain,  N.N.,  S.S.,  N.N.,  S.S.,  which 
would  constitute  a  four-pole  motor,  having  broad 
poles,  and  running  at  a  speed  of  1,500  revolutions 
per  minute. 

Special  switch  gear  is  necessary  to  effect  the  change 
in  the  number  of  poles,  and  the  extra  complication 
is  somewhat  expensive,  so  that  the  method  is  rarely 
employed  in  actual  practice ;  but  in  cases  where  it 
is  applicable,  it  has  the  advantage  of  being  efficient, 
and,  further,  only  one  motor  is  required,  as  against 
two  for  the  cascade  system  of  control. 

When  fans  are  direct  coupled  to  three-phase 
motors,  only  certain  speeds  are  possible,  depending 
upon  the  frequency  of  the  supply,  and  the  number 
of  poles  on  the  motor,  full  particulars  of  which  are 
given  in  Chapter  VII,  dealing  with  electrically  driven 
pumps,  and  to  which  the  reader  is  referred. 


CHAPTER    X 
ELECTRIC  WINDING 

WITHIN  the  last  ten  years  there  has  been  a  great  deal 
of  discussion  as  to  whether  main  winding  by  means 
of  electric  power  is  commercially  practicable.  Col- 
liery managers  who  have  adopted  electric  power  for 
hauling,  pumping,  ventilating,  and  coal  cutting,  have 
hesitated  to  instal  electric  winding  engines  for  main 
winding. 

On  the  Continent  progress  has  been  more  rapid, 
and,  consequently,  there  are  a  large  number  of  main 
winding  engines  abroad,  in  regular  service,  demon- 
strating that  electric  power  can  be  used  with  economy 
and  real  success  for  this  class  of  work. 

The  only  competitor  is  the  steam  winding  engine, 
which  has  now  been  in  use  for  so  many  years,  and 
may  still  be  seen  in  most  of  our  British  collieries. 
But  one  by  one  we  hear  of  electric  winding  engines 
being  installed,  and  there  is  no  doubt  that,  as  the 
merits  of  the  electric  winder  become  more  fully 
recognized,  it  will  be  adopted  for  all  our  important 
collieries. 

A  great  deal  has  been  written  on  this  subject ;  but 
mostly  on  the  question  of  electric  versus  steam  wind- 
ing, and  it  is  not  intended  to  discuss  the  relative 
merits  of  the  two  systems  here.  Suffice  it  that  it 
has  been  proved  that  electric  winding  is  decidedly 
more  economical  for  all  important  collieries,  dealing 
with  a  good  class  of  coals  ;  but  it  is  questionable 
whether  it  would  pay  to  put  down  an  expensive  plant 


ELECTRIC  WINDING 


135 


to  deal  with  coal  which  has  only  a  small  market 
value.  In  such  cases  actual  economy  in  working  is 
less  important,  and  one  can  afford  to  use  such  coal 
uneconomically  for  raising  steam. 

The  subject  of  electric  winding  is  most  interesting 
because  of  the  peculiar  nature  of  the  problems  in- 
volved. It  will  be  seen  that  the  principal  difficulty 


\ 


\ 


30 


40 


60  Sees 


FIG.  30.     WINDING  ENGINE  LOAD  CURVE. 

lies  in  the  widely  fluctuating  load,  which  may  vary 
from  zero  to  2,000  H.P.  or  more,  in  a  few  seconds 
according  to  the  weight,  speed  of  winding,  and 
acceleration. 

The  curve,  Fig.  30,  conveys  a  good  idea  of  the 
load  variation  in  actual  practice,  and  it  will  be  seen 
that  the  conditions  are  not  ideal  from  an  electrical 
standpoint.  In  order  to  take  care  of  the  widely 


136   ELECTRICAL  MINING  INSTALLATIONS 

fluctuating  load,  and  preserve  as  nearly  as  possible 
a  steady  load  on  the  generating  plant,  all  main  wind- 
ing systems  of  any  size  include  what  is  known  as  an 
"  equalizer,"  or  a  flywheel  storage  system  as  described 
later  on. 

Let  us  first  consider  the  case  of  a  winding  plant 
where  the  power  required  is  comparatively  small 
and  where  a  simple  motor  and  controller  can  be 
adopted  without  a  load  equalizer.  The  leading 
particulars  are  usually  obtained  in  the  following 
form  : — 

Depth  of  shaft 400  feet 

Total  amount  of  coal  per  day  .          .      260  tons. 

No.   of  working  hours  per  day  .  .      8  hours. 

There  are  obviously  several  ways  in  which  the  above 
conditions  may  be  complied  with  ;  but  for  the  pur- 
poses of  our  calculation,  we  will  assume  that  it  has 
been  decided  to  allow  55  seconds  for  each  wind,  that 
is,  say,  65  winds  per  hour.  It  will  thus  be  necessary 
to  raise  10  cwt.  of  coal  at  each  wind,  in  order  to  bring 
up  the  260  tons  in  a  working  day  of  eight  hours. 

These  particulars,  together  with  the  weight  of  the 
cage,  hutches,  and  rope,  may  then  be  put  down  as 
follows  : — 

ASCENDING   LOAD    AT    COMMENCEMENT    OF   WIND. 

Weight  of  rope  .  .  .  .  .10  cwt. 
Weight  of  cage  and  hutches  .  .  .15  cwt. 
Weight  of  coal 10  cwt. 


Total     .          .          .          .35  cwt. 

DESCENDING  LOAD  AT  COMMENCEMENT  OF  WIND. 

Weight  of  rope         .....        0 
Weight  of  cage  and  hutches     .          .          .15  cwt. 


Total     .          .          .  .15  cwt. 


It  will  next  be  necessary  to  consider  the  speed  of 
winding  and  acceleration  of  the  load.  Bearing  in 
mind  that  this  is  a  small  winder,  and  that  we  are 


ELECTRIC  WINDING  137 

only  employing  a  simple  motor  and  controller,  with- 
out any  equalizer  or  flywheel  storage,  it  will  be  as 
well  to  allow  as  long  a  period  as  possible  for  accelera- 
tion, in  order  to  prevent  any  wide  variations  of  load 
on  the  generating  plant. 

Assuming  that  ten  seconds  will  be  required  at  the 
end  of  each  wind  for  loading  and  unloading,  this  will 
leave  forty-five  seconds  for  the  actual  wind,  which 
corresponds  to  an  average  winding  speed  of  535  ft. 
per  minute. 

We  therefore  set  these  particulars  down  as  fol- 
lows :• — 

No.  of  winds  per  hour     .          .65. 
Time  required  for  each  wind    .      55  seconds. 
Time  required  for  banking        .      10  seconds. 
Time  required  for  actual  wind       45  seconds. 
Average  winding  speed     .          .      535  ft.  per  minute. 

The  next  thing  to  decide  is  how  to  proportion  the 
time  for  acceleration,  full  speed  period,  and  retarda- 
tion, which,  together,  make  up  forty-five  seconds. 
Bearing  in  mind  that  we  wish  to  prevent  any  wide 
variations  in  load  on  the  generating  plant,  it  will 
suffice  to  allow  ten  seconds,  twenty-five  seconds, 
and  ten  seconds  respectively  for  the  three  operations 
named  above.  From  these  we  are  now  able  to  cal- 
culate the  actual  acceleration,  the  maximum  winding 
speed,  and  the  horse-power  required  at  all  periods 
throughout  the  wind. 

The  calculation  necessary  to  arrive  at  the  horse- 
power required  at  various  points  during  the  wind  is 
somewhat  complicated  by  the  rope,  which  is  all 
against  the  motor  at  the  commencement  of  the  wind  ; 
but  which  is  gradually  passing  from  the  ascending 
load  over  to  the  descending  load,  and  may  in  some 
instances  actually  assist  the  motor  towards  the  end 
of  the  wind. 

The  best  way  to  deal  with  the  matter  is  by  plotting 
a  curve,  and  we  will  now  calculate  the  horse-power 
required  at  four  points  of  the  curve.  The  maximum 


138   ELECTRICAL  MINING  INSTALLATIONS 

horse-power  occurs  at  the  end  of  the  acceleration 
period,  and  is  composed  of  the  horse-power  required 
for  acceleration,  plus  that  required  for  lifting  the 
load  at  the  maximum  winding  speed,  which  we  have 
yet  to  determine.  If  the  acceleration  and  retarda- 
tion are  constant,  it  is  evident  that  the  average  speed 
of  winding  during  these  periods  is  equal  to  half  the 
maximum  winding  speed,  and  that  the  distance 
traversed  by  the  load  will  be  equal  to  half  the  maxi- 
mum speed  multiplied  by  the  time. 

From  this  we  can  find  the  maximum  winding  speed. 

Total  length  of  wind. 

Half  acceleration  period  -j-  full  speed  period  +  half 
retardation  period. 

In  our  case  this  will  be  as  follows  : — 

400  ft.  which  equals  114  ft.  per  second,  or  690 
5  +  25  +  5  ft.  per  minute. 

As  the  distance  traversed  during  acceleration  is  equal 
to  half  690  ft.  per  minute,  multiplied  by  ten  seconds, 
we  find  that  57-5  ft.  of  rope  will  have  been  transferred 
from  one  side  of  the  system  to  the  other  at  the  point 
where  maximum  horse-power  occurs,  that  is,  at  the 
end  of  the  acceleration  period. 

A  weight  corresponding  to  this  length  of  rope  must 
therefore  be  subtracted  from  one  side  and  added  to 
the  other. 

If  400  ft.  of  rope  weigh  10  cwt.,  57-5  ft.  equals 
144  cwt.,  which  leaves  8'56  cwt.  on  the  side  with 
the  load. 

The  loads  to  be  dealt  with  at  this  point  will  be  as 
follows  : — 

Ascending.  Descending. 

Weight  of  rope       .          .        8-56  cwt.  1-44  cwt. 

Weight  of  cages  and  hutch     15  cwt.  15  cwt. 

Weight  of  coal        .          .10  cwt.  0  cwt. 


Totals  33-56  cwt.  16-44  cwt. 

Difference  in  loads  17*12  cwt.  =  1,920  Ib.  approxi- 
mately. 


ELECTRIC  WINDING  139 


TT  P    remiired  —  1'920  lb'  X  69°  ft- 
H.P.  requi  - 


min- 


33,000  fOb.  per  min. 
3—40  H.P.  approximately. 

We  now  want  to  calculate  the  horse-power  required 
for  acceleration.  Since  we  obtain  a  speed  of  690  ft. 
per  minute  in  ten  seconds,  the  acceleration  is  690  -f- 
10  =  69  ft.  per  minute  per  second,  or  say  1-15  ft. 
per  second  per  second. 

Now  from  elementary  principles  of  mechanics  we 
know  that  a  force  of  1  lb.,  acting  on  a  mass  of  1  lb., 
will  produce  an  acceleration  of  approximately  32  ft. 
per  second  per  second,  so  that  in  our  case  the  pull 
on  the  rope,  due  to  acceleration,  will  be  :  Equal  to 
the  total  mass  of  the  two  cages,  the  whole  of  the 
rope,  plus  the  coal,  multiplied  by  the  acceleration  of 
the  load,  and  divided  by  the  acceleration  due  to 
gravity. 

That  i..g'flOOU>-xl-18=  200  lb. 
9ua 

The  horse-power,  at  full  speed,  required  for  accelera- 
tion will  be  :  — 

200  lb.  x  690  ft.  per  min.  _  4.2  jj  P 
33,000  ft.-lb.  per  min. 

The  above  figures  represent  theoretical  results,  and 
the  horse-power  due  to  gravity  must  be  increased  to 
allow  for  friction,  while  the  horse-power  due  to 
acceleration  must  be  increased  to  allow  for  the  inertia 
of  the  drums  and  gears  of  the  winding  engine,  as  well 
as  the  pit  head  sheaves,  and  a  certain  amount  of 
extra  rope.  In  an  important  case  it  would  be  neces- 
sary to  calculate  these  items  separately,  and  add 
them  to  the  total  ;  but  in  this  case  the  amounts  in- 
volved are  small  and  we  can  make  an  allowance  for 
same. 

In  this  case  we  can  assume  an  efficiency  of  70  per 
cent,  for  the  winding  engine,  which  will  cover  the 
friction  of  the  rope  and  guides,  while  we  will  increase 


140  ELECTRICAL  MINING  INSTALLATIONS 

the  horse-power  due  to  acceleration  by  40  per  cent, 
to  cover  the  inertia  of  the  parts  not  taken  into  account 
in  the  foregoing  calculation. 

This  makes  horse-power  due  to  gravity  =  approxi- 
mately 37  H.P.,  and  the  horse-power  due  to  accelera- 
tion =  6  H.P. 

The  total  of  these  results  gives  us  the  first  point 
(a)  on  the  curve  (Fig.  30),  while  the  second  point  (b) 
is  that  corresponding  to  the  horse-power  due  to 
gravity  only. 

The  next  point  to  calculate  is  the  horse  power  at 
the  end  of  the  full  speed  period,  and  to  obtain  this 
we  must  first  ascertain  the  load  on  each  side  of  the 
system.  Proceeding  as  before,  we  obtain  the  loads 
to  be  dealt  with  at  this  point  as  follows  :• — 

Ascending.  D  escending. 

Weight  of  rope           .          .1-44  cwt.  8-56  cwt. 

Weight  of  cages  and  hutches  15  cwt.  15  cwt. 

Weight  of  coal           »         .10  cwt.  0  cwt. 


Totals  26-44  cwt.  23-56  cwt. 

Difference  in  loads,  2-88  cwt.  =  322  Ib.  approximately. 

H.P.  required  =  gggJ^XjOO  ft.  per  min. 

33,000  ft.-lb.  per  min. 
=  6*7  H.P.  approximately. 

Allowing  60  per  cent,  efficiency  at  this  point,  we 
obtain  11  H.P. 

This,  then,  is  the  third  point  (c)  on  our  curve. 

After  this,  power  is  cut  off,  the  brakes  are  applied, 
and  the  retardation  period  begins.  The  horse-power 
must  now  be  considered  as  having  a  negative  value. 

The  horse-power  at  this  point  is  entirely  due  to 
the  inertia  of  the  load,  together  with  the  drums  and 
gears,  pit  head  sheaves,  etc.,  and  may  be  calculated 
in  exactly  the  same  manner  as  given  above  for  ac- 
celeration. In  our  particular  case,  however,  we  have 
taken  the  same  length  of  time  for  acceleration,  as  for 
retardation,  and  the  horse-power  will  therefore  be 


ELECTRIC  WINDING  141 

the  same,  namely,  6  H.P.,  including  the  inertia  of 
the  drums,  gears,  pit  head  sheaves,  etc.  This,  being 
reckoned  as  negative  power,  is  plotted  below  the  zero 
line,  as  shown  in  the  complete  curve  Pig.  30. 

Owing  to  the  particularly  low  speed  of  winding 
chosen,  it  will  be  seen  that  there  will  be  insufficient 
kinetic  energy  in  the  system  to  bring  the  load  to  rest 
at  the  proper  place,  if  the  current  is  cut  off  at  the 
point  marked  ;  and  it  will  therefore  be  necessary,  if 
these  values  are  adopted,  to  reduce  the  power  gradu- 
ally, as  the  load  approaches  its  destination,  the  cur- 
rent being  cut  off  and  the  brakes  applied  within  four 
or  five  seconds  only  of  the  end  of  the  wind. 

All  winding  engines  are  provided  with  a  depth 
indicator,  so  that  the  driver  can  see  at  a  glance  the 
position  of  the  cages,  and,  from  this,  he  knows  when 
to  cut  off  his  current  and  apply  the  brakes. 

The  above  example  represents  a  very  simple  case, 
but  the  method  adopted  will  be  the  same  for  all. 
The  shape  of  the  curve  will,  however,  vary  greatly 
according  to  circumstances.  For  instance,  with  a 
high  winding  speed,  and  a  short  acceleration  period, 
the  curve  would  have  a  very  high  peak  at  starting, 
while,  with  a  very  deep  pit,  the  weight  of  the  rope 
may  be  sufficient  to  assist  the  motor  towards  the  end 
of  the  winding  period,  and  the  brakes  will  not  only 
have  to  absorb  the  kinetic  energy,  but  will  have  to 
bring  the  load  to  rest  against  the  extra  pull  of  the 
descending  cage  and  rope. 

With  very  deep  pits  the  great  length  and  weight 
of  the  ropes  against  the  load  at  starting  puts  a  big 
strain  on  the  motor  and  generating  plant,  and,  for 
this  reason,  it  is  sometimes  customary  to  balance  the 
main  rope  by  a  tail  rope  below  the  cages.  Another 
method  is  to  use  a  conical  drum,  so  that  the  ascending 
load  starts  to  wind  on  a  small  diameter,  while  the 
descending  load  commences  to  unwind  on  a  large 
diameter,  thereby  wholly  or  partially  balancing  the 
unequal  lengths  and  weights  of  the  ropes. 


142   ELECTRICAL  MINING  INSTALLATIONS 

In  our  example  we  assumed  a  parallel  drum,  which 
is  the  pattern  usually  adopted  ;  but,  for  a  very  deep 
pit,  the  parallel  drum  has  to  be  of  considerable  dia- 
meter in  order  to  accommodate  the  necessary  amount 
of  rope,  for  it  is  unusual  to  arrange  the  rope  in  more 
than  one  layer  on  the  drum.  If  the  drum  is  too 
wide  there  is  difficulty  on  account  of  the  angularity 
of  ropes  and  head  gear  pulleys,  and  this  has  a  detri- 
mental effect  on  the  life  of  the  ropes. 

Fig.  31  shows  the  various  types  of  drum  designed 
to  overcome  these  objections. 

"  A  "  is  the  plain  parallel  drum,  which  is  the 
simplest  pattern,  the  ropes  being  wound  in  opposite 
directions  so  that  one  unwinds  as  the  other  winds  up. 

"  B  "  shows  the  conical  drum,  which  commences 
to  wind  the  full  cage,  and  long  rope,  on  a  small  dia- 
meter while  the  empty  cage  and  short  rope  are  sus- 
pended on  the  large.  The  diameters  of  this  type  of 
drum  are  so  chosen  that  the  ropes  will  balance 
throughout  the  whole  of  the  winding  period.  The 
chief  objection  to  the  type  is  its  large  diameter  and 
great  weight,  which  of  course  make  the  drum  itself 
very  expensive,  while  all  the  energy  put  into  the 
drum  at  starting  to  bring  it  up  to  speed  must  be 
wasted  by  braking  when  bringing  the  load  to  rest. 

"  G "  depicts  the  spiro-parallel  drum,  which  is 
really  a  compromise  between  the  conical  and  the 
parallel  patterns.  It  is  practically  a  parallel  drum, 
but,  at  either  end,  there  will  be  a  few  turns  of  the 
rope  on  the  small  diameter,  which  quickly  ascends 
to  the  parallel  part  of  the  drum  in  three  or  four  revo- 
lutions. The  heavy  load  starts  to  wind  up  on  the 
small  diameter,  while  the  light  load  winds  off  the 
large  diameter.  The  ropes  will  not  be  balanced 
throughout  the  wind  as  with  the  conical  drum,  but 
the  conditions  are  in  favour  of  starting  at  the  com- 
mencement, and  also  in  favour  of  stopping  at  the 
end  of  the  wind.  The  drum  is  smaller  in  diameter, 
lighter,  and  cheaper  than  the  conical  drum. 


ELECTRIC  WINDING  143 

"  D  "  shows  the  Keope  pulley  which  has  the  merits 


FIG.   31.     TYPES  OF  WINDING  DRUMS. 

of  simplicity  and  of  light  weight.     It  consists  of  a 
simple  grooved  pulley  in  which  the  rope  lies,  one  cage 


144  ELECTRICAL  MINING  INSTALLATIONS 

being  attached  to  each  end  of  the  rope,  and  balancing 
effected  by  means  of  tail  ropes.  The  system  has 
not  been  used  in  this  country  because  of  the  possi- 
bility of  the  rope  breaking,  in  which  case  there  is 
nothing  to  save  both  cages  from  falling.  Other 
modifications  have  been  tried,  one  of  which  is  known 
as  the  "  Whitting  "  system,  but  it  is  not  likely  to 
come  into  use  in  this  country  for  collieries. 

"  E  "  indicates  the  reel  drums  as  used  on  the  Con- 
tinent. In  this  case  the  ropes  are  flat  and  can  be 
arranged  to  balance,  while  the  drums  are  com- 
paratively light. 

With  electric  winding  engines  the  shape  of  the 
drum  determines,  to  a  great  extent,  the  shape  of  the 
horse-power  curve,  and  also  the  maximum  loads  that 
are  likely  to  occur  on  the  motors  and  generating 
plant. 

The  speed  and  acceleration  also  have  a  great  in- 
fluence in  determining  the  shape  of  the  horse-power 
curve  ;  and  all  these  points  can  only  be  decided  upon 
for  any  particular  installation,  when  full  particulars 
of  the  duty  required  and  limitations  of  the  mine  are 
available. 

Briefly,  the  chief  object  is  to  bring  up  the  required 
amount  of  coal  in  the  given  time,  with  as  small  an 
expenditure  of  energy  as  possible,  consistent  with 
maintaining  a  good  average  continuous  load  on  the 
generating  plant. 

In  most  cases  it  is  only  possible  to  arrive  at  the 
best  solution  after  several  trials  on  paper  ;  but  before 
one  can  attempt  the  problem,  full  particulars  regard- 
ing the  capacity  and  limitations  of  the  mine  must 
be  available. 

Most  mines  in  this  country  are  considerably  deeper 
than  that  in  our  example,  and,  in  order  to  bring  up 
the  full  amount  of  coal  in  the  given  time,  quick  wind- 
ing speeds  and  high  rates  of  acceleration  must  be 
adopted.  The  amount  of  coal  that  can  be  brought 
up  at  a  time  is  limited  by  the  capacity  of  the  trucks 


ELECTRIC  WINDING  145 

used,  this  capacity  being  dependent  upon  the  thick- 
ness of  the  seams  worked. 

The  diameter  of  the  shaft  determines  the  number 
of  trucks  per  deck,  while  the  method  of  handling 
the  trucks  fixes  the  time  required  at  each  wind  for 
changing. 

In  a  deep  mine  a  rope  speed  of  forty  miles  an  hour 
is  not  uncommon,  while  the  acceleration  may  be  6  ft. 
per  second  per  second.  An  electric  winding  engine 
to  deal  with  a  heavy  load  under  such  conditions 
presents  a  difficult  problem,  and  several  patented 
systems  have  been  brought  out,  the  chief  feature  of 
which  is  the  flywheel  storage  plant.  With  this  ar- 
rangement, the  generating  plant  runs  under  approxi- 
mately even  load  all  day,  the  heavy  demand  for  power 
during  the  acceleration  period  being  taken  from  the 
flywheel  set,  this  energy  being  put  back  during  the 
time  current  is  not  required  on  the  winding  motor, 
thereby  preserving  an  approximately  even  load  on  the 
generating  plant. 

Motors  operating  electric  winding  engines  may  be 
of  the  continuous  current,  three-phase,  or  two-phase 
type.  If  the  plant  is  simple,  the  motors  may  be 
controlled  by  means  of  a  standard  controller  as  de- 
scribed for  haulage  gears.  One  point  must  not  be 
lost  sight  of  in  connexion  with  the  design  of  the 
resistances.  They  must  allow  of  running  the  motors 
at  a  suitable  speed  for  lowering  and  raising  the  men, 
and  they  should  also  be  capable  of  giving  a  very  slow 
speed  for  examining  the  shaft. 

The  brake  gear  must  necessarily  be  well  designed, 
and,  in  addition  to  the  ordinary  service  brake,  an 
emergency  brake  is  usually  provided,  this  being  set 
in  action  by  the  winding  indicator  if  the  driver  fails 
to  stop  the  cages  in  time.  It  is  also  usual  for  the 
emergency  brake  to  come  into  operation  when  the 
speed  exceeds  a  predetermined  limit. 


CHAPTER    XI 
ELECTRIC  WINDING  SYSTEMS 

As  already  pointed  out  in  the  previous  chapter,  all 
electric  winding  plants  (except  very  small  installa- 
tions, operating  under  the  most  advantageous  cir- 
cumstances as  regards  winding)  would  give  rise  to  a 
load  curve  of  an  objectionable  description  as  viewed 
from  the  generating  station  point  of  view. 

With  the  idea  of  obtaining  the  most  advantageous 
conditions  of  winding,  together  with  a  more  or  less 
even  load  on  the  generating  plant,  several  electric 
winding  systems  have  been  developed.  In  all  cases 
the  main  principle  is  the  same,  namely,  that  of  stor- 
ing energy  during  such  times  as  there  is  little  or  no 
load  on  the  winding  engine,  this  energy  being  given 
up  again  at  the  time  of  greatest  need  (i.e.  during 
acceleration)  to  assist  the  main  generators.  With 
a  properly  designed  system,  working  under  such 
conditions,  the  main  generating  plant  will  run 
continuously  throughout  the  working  day  under 
approximately  constant  load. 

The  various  systems  differ  in  their  manner  of 
storing  the  energy,  but  most  makers  use  a  heavy 
flywheel ;  although  secondary  batteries  have  been 
proposed,  and  have  some  advantages. 

We  will  deal  first  with  the  flywheel  storage  systems. 
It  is  well  known  that  the  energy  stored  in  a  revolving 
flywheel  is  given  by  the  formula  M  X  V2  -f-  2. 

Where  M  =  the  mass  of  the  rim  (Ib.  ~  32 '2),  and 
V  —  the  velocity  in  feet  per  second. 

The  result  is  in  foot-pounds  of  energy  stored  in 


ELECTRIC  WINDING  SYSTEMS         147 

the  wheel.  From  this  it  will  be  seen  that  the  energy 
is  proportional  to  the  weight  of  the  rim  of  the  wheel 
and  to  the  square  of  its  speed.  These  flywheels  are 
usually  made  of  steel  plate,  and  are  run  at  as  high  a 
speed  as  possible,  consistent  with  safety. 

It  is  evident  that  while  a  flywheel  runs  at  constant 
speed,  no  energy  is  added  to  or  taken  from  the  sys- 
tem. In  order  to  take  any  energy  out  of  the  wheel 
the  speed  must  be  decreased,  and,  conversely,  if 
energy  be  added  to  the  wheel  the  speed  is  increased. 

In  adapting  this  principle  to  electric  winding  plants, 
we  alternatively  store  energy  in  and  extract  it  from  the 
wheel,  the  speed  varying  accordingly.  The  useful 
work  put  into  or  taken  from  the  system  depends 
upon  the  difference  between  maximum  and  minimum 
speeds,  and  is  given  by  the  formula  : — 

M  (V2  —  v2)  -^  2  =  foot-lbs. 

A  calculation  based  on  any  case  in  practice  will  show 
at  once  that  it  requires  a  very  heavy  wheel,  running 
at  a  good  speed,  to  obtain  the  desired  results,  because 
it  is  not  possible  to  have  too  great  a  variation  be- 
tween the  maximum  and  minimum  speeds  of  the 
flywheel  storage  set. 

The  above  represents  the  problem  from  a  mechani- 
cal point  of  view,  and  it  is  chiefly  in  connexion  with 
the  methods  of  driving  the  flywheel  set  electrically, 
and  regulating  its  speed  according  to  the  demand, 
that  the  various  systems  now  described  have  been 
evolved. 

Perhaps  the  best  known  is  the  Siemens-Ilgner 
System,  which  has  been  developed  by  Messrs.  Siemens 
Schuckertwerke  in  Germany,  and  Messrs.  Siemens 
Brothers  Dynamo  Works,  Limited,  in  this  country. 

The  diagram,  Fig.  32,  illustrates  the  general  fea- 
tures. From  the  mains,  or  from  an  electric  power 
station,  is  drawn  the  current  for  driving  a  motor 
generator  or  converter,  consisting  of  a  motor  coupled 
to  a  dynamo. 


148   ELECTRICAL  MINING  INSTALLATIONS 

This  converter  transforms  the  supply  current  into 
continuous  current  at  variable  voltage,  which  is  used 
for  driving  the  winding  motor.  The  supply  may  be 
either  alternating  on  the  two-or  three-phase  system, 
or  continuous  current,  whichever  happens  to  be 
available  from  power  station  or  supply  company. 

The  converter  motor  is  built  to  suit  the 
character  of  the  supply,  but  the  diagram,  Fig.  32, 
shows  a  three-phase  motor  with  slip  rings,  the  starting 
panel  with  main  switches  being  at  (a)  and  the  rotor 
starting  resistance  at  (c). 

The  converter  is  provided  with  a  heavy  flywheel 
in  the  form  of  a  single  steel  casting,  or  forging,  which 
is  capable  of  running  with  safety  at  a  high  circum- 
ferential velocity.  The  energy  stored  in  this  fly- 
wheel is  drawn  upon  for  taking  up  fluctuations  in 
the  load  of  the  winding  engine,  and  equalizing  the 
load  upon  the  generating  plant. 

The  converter  generator  and  the  winding  motor 
are  both  of  the  continuous-current  type.  They  are 
separately  excited,  and,  when  the  supply  is  alternat- 
ing, a  small  direct-coupled  dynamo  provides  the 
necessary  excitation  current. 

The  armatures  of  the  winding  motor  and  the  con- 
verter generator  are  connected  in  series,  and  a  set 
of  regulating  resistances  is  provided,  by  means  of 
which  the  exciting  current  of  the  converter  generator 
is  varied  from  zero  to  a  positive  or  negative  maxi- 
mum. The  degree  of  excitation  determines  the 
voltage  generated,  and  applied  to  the  terminals  of 
the  winding  motor  armature,  and  the  revolutions  of 
the  latter  vary  in  direct  proportion. 

The  winding  motor  is  either  direct-coupled  to  the 
drum,  or  drives  through  single-reduction  spur  gearing. 
The  former  has  the  advantage  of  simplicity  of  con- 
struction, and  freedom  from  noise  when  working, 
and  is  generally  used  for  all  plants  of  large  size  ;  for 
smaller  plants,  however,  it  is  more  costly  than  the 
geared  arrangement.  In  very  large  plants,  two 


ELECTRIC  WINDING  SYSTEMS        149 

coupled  motors,  one  on  either  side  of  the  winding 


Flywheel   Converter 

rr 


FlG.    32.       SlEMENS-lLGNER   WINDING   SYSTEM. 


drum,    are    sometimes   used.     This   arrangement   is 
chiefly  advantageous  in  giving  extra  security  against 


150  ELECTRICAL  MINING  INSTALLATIONS 

breakdown  since,  in  an  emergency,  one  motor  can  be 
used  to  wind  at  half  speed. 

As  already  mentioned,  the  complete  system  is  con- 
trolled by  the  regulating  apparatus,  a  control  lever 
being  provided  for  working  the  field  rheostat  in  the 
excitation  circuit  of  the  converter  generator.  As 
this  field  rheostat  controls  the  excitation  current 
from  zero  to  a  positive  or  negative  maximum,  it  is 
evident  that  reversal  of  the  winding  motors  is  effected 
by  moving  the  control  lever  to  one  side  or  the  other 
from  its  "  off  "  position.  This  regulator  is  provided 
with  a  large  number  of  steps,  in  both  directions,  so 
that  exceedingly  small  gradations  of  speed  are  ob- 
tainable. By  moving  the  controller  only  a  small 
amount  from  the  central  position,  the  cages  can  be 
driven  at  a  creeping  speed  which  is  necessary  for 
inspecting  the  shaft.  By  moving  the  control  lever 
a  greater  distance,  the  acceleration  and  winding 
speed  are  increased  to  any  desired  and  predetermined 
value  for  which  the  plant  may  be  designed. 

Another  special  feature  of  the  system  is  the  "  re- 
generative braking."  Assume  the  engine  to  be  in 
operation,  and  winding  at  full  speed  ;  then,  by  mov- 
ing the  control  lever  back  toward  the  central  posi- 
tion, the  excitation  of  the  converter  motor-generator 
is  reduced,  until  its  electro-motive  force  falls  below 
the  back  electro-motive  force  of  the  winding  motors. 
The  latter  act  as  generators,  and  tend  to  bring  the 
gear  to  rest,  while,  at  the  same  time,  it  replenishes 
energy  and  increases  the  speed  of  the  flywheel  set. 

In  addition  to  this  regenerative  braking  action  other 
brakes  are  used,  similar  to  those  employed  with  steam 
winding  engines,  except  that  they  are  operated  by 
compressed  air,  supplied  by  a  small  electrically 
driven  compressor. 

Fig.  33  shows  an  actual  load  diagram,  taken  from 
an  electric  winding  engine.  The  high  peaks,  at  the 
commencement  of  each  cycle,  show  the  power  taken 
during  the  acceleration  periods,  while  the  other  curve 


ELECTRIC  WINDING  SYSTEMS        151 


152   ELECTRICAL  MINING  INSTALLATIONS 

shows  how  the  load  has  been  maintained  approxi- 
mately constant  on  the  generating  plant,  all  the 
time  the  winding  engine  is  in  use. 

As  an  illustration  of  an  electric  winding  system 
employing  secondary  batteries  as  load  equalizer  we 
may  instance  that  designed  by  Messrs.  Crompton 
and  Co.  The  diagram,  Fig.  34,  shows  the  arrange- 
ment of  the  connexions.  In  this  particular  case  a 
three-phase  supply  is  shown,  but  it  will  obviously 
make  no  difference  to  the  principle,  if  the  supply  be 
on  any  other  system. 

There  are  two  continuous  current  motors,  direct 
coupled  to  the  winding  drums.  The  armatures  of 
these  motors  are  connected  in  series,  and  provided 
with  a  reversing  switch,  the  position  of  which  deter- 
mines the  direction  in  which  they  should  run. 

The  fields  have  two  separate  exciting  coils,  one 
being  connected  between  the  main  leads  from  the 
omnibus  bars  in  the  generating  station,  and  the  other 
from  a  point  between  the  armatures  of  the  two 
motors  to  one  of  the  leads  from  the  omnibus  bars. 

These  motors  are  supplied  with  energy  through 
a  special  motor  generator,  the  function  of  which  is 
to  give  automatic  and  hand  control  over  the  voltage 
at  the  terminals  of  the  motors,  without  the  necessity 
or  troublesome  and  wasteful  series  resistances,  and, 
consequently,  to  give  a  very  wide  range  of  control 
over  the  motor  speeds. 

The  motor  generator  consists  of  two  continuous- 
current  machines,  one  being  an  ordinary  shunt 
motor  supplied  with  power  from  the  mains. 

This  special  generator  is  in  series  with  the  main 
source  of  supply,  and  is  consequently  able  to  increase 
or  diminish  the  voltage  of  the  main  supply,  accord- 
ing to  whether  it  is  excited  in  one  direction  or  the 
other ;  and,  by  special  windings,  is  able  to  give  a 
wide  range  of  hand  control  as  well  as  an  automatic 
control,  over  the  volts  added  to  or  deducted  from 
the  main  supply. 


ELECTRIC  WINDING  SYSTEMS         153 


FIG.  34.     CROMPTON  WINDING  SYSTEM. 


154  ELECTRICAL  MINING  INSTALLATIONS 

To  produce  this  result  the  generator  portion  of  the 
motor  generator  has  two  field  windings,  one  being  a 
separately  exciting  circuit,  taken  from  the  main 
omnibus  bars  through  the  agency  of  a  reversing  and 
regulating  switch,  which  gives  a  full  range  of  adjust- 
ment between  a  maximum  in  one  direction  down  to 
zero,  and,  further,  to  a  maximum  in  the  opposite 
direction. 

This  field  excitation  is  supplemented  by  a  special 
limiting  coil,  connected  in  series  with  the  generator 
and  the  motors,  and  wound  in  such  a  direction  that, 
by  partially  or  entirely  neutralizing  the  supply  voltage 
it  entirely  prevents  the  current  through  the  motors, 
under  any  circumstances,  from  exceeding  a  definite 
pre-determined  amount. 

The  motor-generator  and  motors  take  their  power 
from  any  ordinary  continuous-current  generating 
plant,  which,  however,  should  preferably  be  pro- 
vided with  a  storage  battery,  and  automatic  rever- 
sible booster,  as  used  in  tramway  stations. 

The  diagram  above  referred  to  illustrates  the  case 
of  a  three-phase  supply  system,  in  which  it  becomes 
necessary  to  provide  another  motor-generator  set  to 
convert  three-phase  current  into  medium  tension 
continuous  current.  A  small  storage  battery  is  used 
in  parallel  with  the  continuous-current  machine,  and 
the  fields  of  this  latter  are  wound  in  such  a  way  as  to 
draw  the  extra  current,  required  for  acceleration, 
from  the  battery,  and  not  from  the  supply  source  ; 
also  to  return  the  extra  current,  generated  during 
braking,  to  the  battery  and  not  to  the  supply.  There 
may  be  cases  where  a  storage  battery  is  not  required  ; 
for  instance,  as  the  winding  is  only  a  small  proportion 
of  the  total  continuous  current  load  of  the  colliery,, 
the  return  currents  go  out  to  the  other  machines 
and  simply  relieve  the  main  dynamo  of  its  load ; 
but  in  most  cases  the  battery  is  recommended. 

The  working  of  the  system  is  as  follows  : — 

When  the  cage  is  at  rest  the  reversing  switch  may 


ELECTRIC  WINDING  SYSTEMS        155 

be  in  either  position,  and  the  regulator,  already 
described,  is  in  such  a  position  that  the  motor  genera- 
tor completely  neutralizes  the  supply  voltage  ;  con- 
sequently, although  the  main  circuit  to  the  motors  is 
made,  no  current  flows  through  them,  and  there  is 
no  movement  of  the  cage  ;  in  fact,  the  cage,  under 
these  circumstances,  is  electrically  locked,  and  unable 
to  move. 

When  it  is  desired  to  commence  winding,  the 
reversing  switch  is  set  to  the  required  position,  which 
may  be  done  without  opening  the  main  circuit.  The 
regulator  is  then  moved  so  as  to  allow  the  generator 
to  neutralize  less  of  the  supply  volts,  until  they  attain 
their  maximum  value,  and  afterwards  to  increase 
them  until  their  value  is  doubled. 

It  is  immaterial  whether  this  operation  is  carried 
out  slowly  as  the  motor  speeds  up,  or  quickly,  for  if 
at  any  time  it  is  so  moved  as  to  produce  a  tendency 
for  the  generating  plant  to  give  the  motors  too  much 
current,  the  limiting  coil  on  the  motor  generator 
comes  into  action,  and  at  once  reduces  the  voltage 
and  keeps  the  motor  current  down  to  the  predeter- 
mined amount. 

Under  these  circumstances  the  motors  are  supplied 
with  a  constant  armature  current,  adjusted  to  a 
figure  which  has  been  found  most  suitable  for  giving 
the  acceleration  required  to  bring  the  speed  of  the 
cage  up  to  its  maximum  in  the  shortest  possible  time. 

When  the  cage  is  standing,  the  motor  armatures 
are  receiving  no  current,  but  their  fields  are  at  maxi- 
mum strength.  B  coil  is  constant,  remaining  at  the 
same  strength  under  all  circumstances,  and  C  coil 
under  these  conditions  is  subjected  to  a  voltage  equal 
to  the  supply  voltage,  and  these  two  excitations  give 
full  field  strength,  which  enables  the  armature  to 
hold  the  cage  in  position,  and,  when  required,  gives 
the  maximum  possible  starting  torque.  The  condi- 
tions for  acceleration  are  ideal.  At  first  the  field  is 
at  maximum  strength  and  the  volts  on  the  armatures 


156  ELECTRICAL  MINING  INSTALLATIONS 

automatically  adjusted  to  give  the  required  accelera- 
tion without  the  current  exceeding  the  limiting 
figure. 

It  will  be  noticed  that  accelerating  power  is  ob- 
tained by  increasing  the  field  strength  instead  of  by 
increasing  the  armature  current,  as  in  ordinary 
series-parallel  or  series  motor  systems.  This  makes 
a  great  deal  of  difference  in  the  design  of  the  motor, 
and  enables  the  efficiency  of  the  motor  under  these 
conditions  to  be  at  its  maximum,  besides  dispensing 
with  starting  resistances,  which  are  wasteful. 

When  the  cage  attains  its  full  speed  the  volts  on 
the  armatures  are  double  the  volts  of  the  supply, 
and  the  fields  are  weak  owing  to  the  fact  that  C  coil 
is  now  doing  nothing. 

When  it  is  required  to  reduce  the  speed  and  stop, 
the  regulator  on  the  motor  generator  is  reversed  so 
that  the  voltage  supply  to  the  motors  is  lowered. 
The  motors  will  then  commence  to  run  as  generators 
and  return  current  to  the  generating  plant,  which  is 
either  used  by  other  machines  or  absorbed  by  the 
storage  battery. 

The  fields  of  the  motors  begin  to  strengthen  owing 
to  C  coil  again  coming  into  use,  which  maintains  the 
power  returned  to  the  supply.  This  return  power  is, 
however,  limited  in  the  same  way  as  was  the  accelerat- 
ing current,  owing  to  the  action  of  'the  limiting  coil 
on  the  motor  generator,  so  that  the  return  current 
and  the  braking  effort  are  kept  within  a  certain  pre- 
determined limit. 

Under  these  conditions  the  cage  rapidly  loses  speed 
and  can  be  brought  to  rest  definitely  and  held  in 
position  at  the  proper  place. 

In  the  two  foregoing  systems  of  electric  winding 
it  will  be  noted  that  continuous  current  is  supplied 
to  the  motors  driving  the  winding  drums.  In  the 
Westinghouse  Converter  Equalizer  system  now  des- 
cribed, three-phase  motors  are  used  to  drive  the 
winding  drums.  This  arrangement  has  an  advantage 


ELECTRIC  WINDING  SYSTEMS         157 

over  that  in  which  the  current  is  first  converted  to 
continuous  current,  inasmuch  as  the  winding  motors 
may  still  be  operated  in  the  event  of  the'equalizer  or 
flywheel  set  breaking  down. 

As  shown  in  Fig.  35,  the  general  arrangement  of 


From  Power*  Station  to  Winding  Motor 


FIG.  35.     WESTINGHOTJSE  WINDING  SYSTEM. 


the  Westinghouse  system  consists  of  a  rotary  con- 
verter (1)  connected  through  transformers  (2)  to  the 
transmission  line.  On  its  continuous  current  side 
the  rotary  converter  is  connected  to  a  continuous- 
current  machine  ;  (3)  acting  sometimes  as  a  generator 


158   ELECTRICAL  MINING  INSTALLATIONS 

and  sometimes  as  a  motor,  and  fitted  with  a  fly- 
wheel (4). 

The  rotary  converter  is  compounded  in  a  special 
way  so  as  to  supply,  automatically,  the  magnetizing 
currents  required  by  the  induction  motors  on  the 
system.  The  voltage  of  the  continuous  current  fly- 
wheel machine  (3)  is  controlled  automatically  by  a 
quick  acting  regulating  apparatus  (5)  which  is 
actuated  from  the  transmission  line  through  a  series 
transformer.  The  whole  arrangement  constitutes  a 
*'  converter  equalizer,"  the  action  of  which  is  to  dis- 
charge energy  into  the  high  tension  system  whenever 
the  load  on  the  latter  is  greater  than  the  constant  out- 
put ;  and  to  store  energy  in  the  flywheel  whenever 
the  power  demand  from  the  high  tension  supply 
system  is  less  than  the  constant  output  of  the  station. 

When  there  is  no  load  on  the  high  tension  system, 
the  rotary  converter  runs  with  approximately  100 
per  cent,  power  factor,  and  gives  up  to  the  flywheel — 
through  the  medium  of  the  continuous-current 
machine  acting  as  a  motor — energy  corresponding  to 
the  constant  output  of  the  station,  until  maximum 
speed  is  reached.  The  flywheel  is  built  for  high 
speeds,  in  order  to  obtain  the  necessary  effect  with  a 
minimum  of  weight,  and  the  slip  may  be  anything 
up  to  30  per  cent,  or  40  per  cent,  if  necessary. 

This  converter  equalizer  may  be  applied  to  the 
three-phase  system  at  any  point,  and  three-phase 
current  taken  from  the  system 'will  then  be  governed 
by  it.  In  using  the  equalizer  for  electric  winding 
engines,  three-phase  winding  motors  are  employed, 
and  any  number  may  be  connected  to  the  system  of 
which  the  equalizer  forms  a  part.  Several  electric 
winding  engines  may  therefore  be  put  down  to 
work  in  conjunction  with  one  equalizer,  and,  further, 
the  latter  may  be  placed  in  any  convenient  position 
and  need  not  necessarily  be  installed  in  the  winding 
engine  house. 

It  will  be  evident,  on  further  consideration,  that 


ELECTRIC  WINDING  SYSTEMS         159 

this  system  differs  in  some  important  respects  from 
the  Ilgner  and  Crompton  systems  just  described. 
In  both  these  cases  the  whole  of  the  electrical  energy 
is  converted,  by  means  of  the  motor  generators 
provided,  while  in  the  Westinghouse  converter 
equalizer  system,  only  that  amount  of  energy  is 
transformed  into  continuous  current,  and  back  into 
three-phase  current,  which  is  in  excess  of,  or  below, 
the  constant  output  of  the  station.  It  stands  in  the 
same  relation  to  the  three-phase  system  as  the  air 
chamber  to  a  plunger  pump,  and,  in  like  manner,  the 
system  may  be  operated  at  any  time  without  the 
equalizer  if  necessary. 

In  order  to  clearly  explain  the  operation  of  the 
winding  engine  with  this  system  of  control,  Fig.  36 
has  been  prepared,  partly  perspective  and  also 
diagrammatic.  The  drum  or  friction  brakes  are 
normally  actuated  by  the  compressed  air  cylinder 
(B)  or,  in  cases  of  emergency,  by  the  weighted  lever 
(C).  The  whole  control  gear  is  operated  by  means 
of  three  levers  which  are  fixed  on  the  driver's  platform. 

The  lever  (a)  on  the  driver's  right,  actuates  the 
main  reversing  switch  and  the  liquid  starting  rheostat. 
The  lever  can  be  moved  either  forward  or  backward 
from  its  central  or  off  position,  the  condition  of  the 
main  reversing  switch  (o)  and,  consequently,  the 
direction  of  rotation,  depending  upon  this  movement. 
As  soon  as  the  lever  is  moved,  either  way,  the  main 
reversing  switch  is  first  operated,  and  then  the  liquid 
starting  rheostat. 

The  latter  consists  of  two  tanks,  mounted  one 
above  the  other,  together  with  a  small  motor  and 
circulating  pump  as  shown  in  the  illustration.  The 
upper  tank  contains  three  stationary  electrodes,  and  a 
movable  sluice  gate,  the  electrodes  being  connected 
to  the  slip  rings  of  the  main  motor.  The  lower  tank 
holds  a  supply  of  resistance  liquid,  and  is  fitted  with 
pipes  through  which  cooling  water  is  circulated. 

The  liquid  is  transferred  into  the  upper  tank  by 


160   ELECTRICAL  MINING  INSTALLATIONS 


ELECTRIC  WINDING  SYSTEMS         161 

means  of  the  circulating  pump  and  returns  to  the 
lower,  over  the  sluice  gate,  which  is  in  its  lowest 
position  when  the  driver's  operating  lever  is  off. 

Following  on  the  first  movement  of  the  control 
lever — which  throws  the  main  reversing  switch  into 
one  position  or  the  other,  according  to  the  required  di- 
rection of  rotation — the  sluice  gate  is  raised.  This 
causes  the  level  of  the  liquid  in  the  upper  tank  to 
rise,  and,  consequently,  decreases  the  resistance 
between  the  slip  rings. 

The  sluice  gate  may  be  checked  in  any  position, 
or  it  may  be  immediately  thrown  to  its  highest  point, 
this  depending  on  how  the  driver  operates  his  lever ; 
as,  however,  the  liquid  cannot  follow  the  raised  sluice 
gate  faster  than  the  pump  can  raise  the  liquid  into 
the  upper  tank,  a  certain  maximum  acceleration 
of  the  motor  cannot  be  exceeded,  although  any  less 
acceleration  may  be  obtained.  This  maximum 
acceleration  is  adjustable  by  means  of  a  stop  valve 
in  the  delivery  pipe  of  the  pump. 

The  lever  (b)  on  the  driver's  left,  operates  the 
pneumatic  brake.  The  design  of  the  control  gear 
is  such  that  electrical  braking  of  the  motor,  when 
lowering,  may  be  arranged  for  if  necessary. 

The  foot  lever  (c)  is  placed  in  a  position  between 
the  hand  levers,  so  that  complete  control  is  all  within 
easy  reach  of  the  driver.  This  pedal  releases  the 
weighted  brake  lever,  and  also  opens  the  emergency 
switch  (/),  thus  cutting  off  the  supply  of  current 
tD  the  motor. 

Provision  is  also  made  for  stopping  the  plant  in 
the  event  of  overwinding,  or  a  failure  of  the  electricity 
supply.  The  former  is  effected  by  tripping  mechanism 
in  connexion  with  the  depth  indicator ;  while  an 
abnormal  fall  in  voltage,  or  failure  of  the  supply, 
causes  the  cores  of  solenoid  (H)  to  drop,  and  release 
the  emergency  brake  and  switch. 

Replacement  of  the  weighted  lever  (C)  is  provided 
for  by  means  of  a  small  winch  shown  at  (K). 


162    ELECTRICAL  MINING  INSTALLATIONS 

Although  the  technical  description  of  the  foregoing 
winding  systems  are  somewhat  intricate,  the  actual 
operation  of  such  a  plant,  from  the  driver's  point  of 
view,  is  very  simple.  In  fact,  it  is  simpler  than  the 
steam  winder,  and,  further,  the  protective  and 
emergency  devices  provided,  compel  the  driver  to 
work  his  plant  properly,  while  any  accident  that 
might  possibly  occur  is  safeguarded  to  an  extent 
which  is  impossible  with  the  steam  winder. 


CHAPTER    XII 

Special  rules  for  the  installation  and  use  of  electricity. 

THE  following  Rules  shall  be  observed,  as  far  as  is 
reasonably  practicable,  in  the  mine. 

DEFINITIONS 

The  expression  "  pressure  "  means  the  difference 
of  electrical  potential  between  any  two  conductors 
through  which  a  supply  of  energy  is  given,  or  between 
any  part  of  either  conductor  and  earth,  as  read  by  a 
hot  wire  or  electrostatic  voltmeter  and — 

(a)  Where  the  conditions  of  the  supply  are  such 

that  the  pressure  at  the  terminals  where  the 
electricity  is  used  cannot  exceed  250  volts, 
the  supply  shall  be  deemed  a  low-pressure 
supply. 

(b)  Where  the  conditions  of  supply  are  such  that 

the  pressure  at  the  terminals  where  the 
electricity  is  used,  between  any  two  con- 
ductors, or  between  one  conductor  and  earth, 
may  at  any  time  exceed  250  volts,  but  cannot 
exceed  650  volts,  the  supply  shall  be  deemed 
a  medium-pressure  supply. 

(c)  Where  the  conditions  of  supply  are  such  that 

the  pressure  at  the  terminals  where  the 
electricity  is  used  between  any  two  conduc- 
tors, or  between  one  conductor  and  earth, 
may  at  any  time  exceed  650  volts,  but  cannot 


164  ELECTRICAL  MINING  INSTALLATIONS 

exceed  3,000  volts,  the  supply  shall  be 
deemed  a  high-pressure  supply. 
(d)  Where  the  conditions  of  supply  are  such  that 
the  pressure  at  the  terminals  where  the 
electricity  is  used,  between  any  two  con- 
ductors, or  between  one  conductor  and  earth, 
may  at  any  time  exceed  3,000  volts,  the 
supply  shall  be  deemed  an  extra  high- 
pressure  supply. 


SECTION   I 

GENERAL 

1.  (a)  All  electrical  apparatus  and  conductors 
shall  be  sufficient  in  size  and  power  for  the  work  they 
may  be  called  upon  to  do,  and,  so  far  as  is  reasonably 
practicable,  efficiently  covered  or  safeguarded,  and 
so  installed,  worked,  and  maintained,  as  to  reduce 
the  danger  through  accidental  shock  or  fire  to  the 
minimum  ;  and  shall  be  of  such  construction,  and  so 
worked,  that  the  rise  in  temperature  caused  by 
ordinary  working  will  not  injure  the  insulating 
materials. 

(b)  In  any  place  or  part  of  a  mine  where  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  the  covering  shall  be  constructed  so  that,  as 
far  as  is  reasonably  practicable,  there  is  no  danger 
of  firing  gas  by  sparking  or  flashing,   which   may 
occur  during  the  normal  or  abnormal  working  of  the 
apparatus. 

(c)  AJl    metallic    coverings,    armouring    of   cables, 
other  than  trailing  cables,  and  the  frames  and  bed- 
plates of  generators,  transformers,  and  motors  other 
than  portable  motors  shall,  as  far  as  is  reasonably 
practicable,  be  efficiently  earthed  where  the  pressure 
at  the  terminals  where  the  electricity  is  used,  exceeds 
the  limits  of  low  pressure. 


SPECIAL  RULES  165 

Z.  Where  a  medium-pressure  supply  is  used  for 
power  purposes,  or  for  arc  lamps  in  series,  the  wires 
or  conductors  forming  the  connexions  to  the  motors, 
transformers,  arc  lamps  or  otherwise  in  connexion 
with  the  supply,  shall  be,  as  far  as  is  reasonably 
practicable,  completely  enclosed  in  strong  armouring 
or  metal  casing,  efficiently  connected  with  earth, 
or  they  shall  be  fixed  at  such  a  distance  apart,  or  in 
such  a  manner,  that  danger  from  fire  or  shock  may 
be  reduced  to  the  minimum.  This  rule  shall  not 
apply  to  trailing  cables. 

3.  Where  a  medium-pressure  supply  is  used  for 
incandescent  lamps  in  series,  the  wires  or  conductors 
forming  connexions  to  the    incandescent  lamps,  or 
otherwise  in  connexion  with  the  supply,  shall    be, 
as  far  as  is  reasonably  practicable,  completely  en- 
closed in  strong  armouring  or  metal  casing,  efficiently 
connected  with  earth,  or  they  shall  be  fixed  at  such 
a  distance  apart,  or  in  such  a  manner  that  danger 
from  fire  or  shock  shall  be  reduced  to  the  minimum. 

4.  Motors  of  coal-cutting  and  such  other  portable 
machines  shall  not  be  used  at  a  pressure  higher  than 
medium   pressure.     No    transformer   used   for   sup- 
plying current  at  a  pressure  higher  than  medium 
pressure,  and  no  motor  using  such  current,  shall  be  of 
less  normal  rating  than  20  B.H.P.  for  use  underground. 

No  higher  pressure  than  a  medium  pressure  shall 
be  used  in  any  place  or  part  of  the  mine  to  which 
General  Rule  No.  8  of  the  Coal  Mines  Regulation 
Act,  1887,  applies. 

5.  No    higher    pressure    than    a    medium-pressure 
supply  shall  be  used  other  than  for  transmission  or 
for  motors,  and  the  wires  or  conductors  other  than 
overhead  lines  above  ground,  forming  the  connexions 
to  the  motors  or  transformers,  or  otherwise  in  con- 
nexion with  the  supply,  shall  be  completely  enclosed 
in  a  strong  armouring  or  metal  casing,  efficiently 
connected  with  earth,  or  they  shall  be  fixed  at  such 
a  distance  apart,  or  in  such  a  manner  that  danger 


166  ELECTEICAL  MINING  INSTALLATIONS 

from  fire  or  shock  shall  be  reduced  to  the  minimum. 
The  machines,  apparatus,  and  lines  shall  be  so 
marked  as  to  clearly  indicate  that  they  are  high 
pressure,  either  by  the  use  of  the  word  "  Danger  "  at 
frequent  intervals,  or  by  red  paint  properly  renewed 
when  necessary. 

6.  The  insulation  of  every  complete  circuit  other 
than  telephone  or  signal  wires,  used  for  the  supply  of 
energy,    including    all    machinery,    apparatus,    and 
devices  forming  part  of  or  in  connexion  with  such 
circuit,  shall  be  so  maintained  that  the  leakage  cur- 
rent shall,  so  far  as  is  reasonably  practicable,  not 
exceed   TOW  °f  ^ne  maximum  supply  current,  and 
suitable  means  shall  be  provided  for  the  immediate 
localization  of  leakage. 

7.  In  every  completely  insulated  circuit,  earth  or 
fault  detectors  shall  be  kept  connected  up  in  eveiy 
generating  and  transforming  station,  to  show  imme- 
diately any  defect  in  the  insulation  of  the  system. 
The  readings  of  these  instruments  shall  be  recorded 
daily  in  a  book  kept  at  the  generating  or  transform- 
ing station  or  switch-house. 

8.  Main  and  distribution  switch  and  fuse  boards 
must  be  made  of  incombustible  insulating  material, 
such  as  marble  or  slate  free  from  metallic  veins,  and 
be  fixed  in  as  dry  a  situation  as  practicable. 

9.  Every  sub-circuit  must  be  protected  by  a  fuse 
on  each  pole.     Every  circuit  carrying  more  than  5 
amperes  up  to  125  volts,  or  3  amperes  at  any  pressure 
above  125  volts,  must  be  protected  in  one  of  the 
following  alternative  methods  :• — • 

(a)  By  an  automatic  maximum  cut-out  on  each 
pole. 

(b)  By   a   detachable   fuse   on   each   pole,   con- 
structed in  such  a  manner  that  it  can  be 
removed  from  a  live  circuit  with  the  mini- 
mum risk  of  shock. 

(c)  By  a  switch  and  fuse  on  each  pole. 

10.  Fire  buckets,  filled  with  clean,  dry  sand,  shall 


SPECIAL  RULES  167 

be  kept  in  electrical  machine  rooms,  ready  for  imme- 
diate use  in  extinguishing  fires. 

No  repair  or  cleaning  of  the  live  parts  of  any 
electrical  apparatus,  except  mere  wiping  or  oiling, 
shall  be  done  when  the  current  is  on. 

Gloves,  mats,  or  shoes  of  india-rubber  or  other 
non-conducting  material  shall  be  supplied  and  used 
where  the  live  parts  of  switches  or  machines  working 
at  a  pressure  exceeding  the  limits  of  low  pressure, 
have  to  be  handled  for  the  purpose  of  adjustment. 

11.  A  competent  person  shall  be  on  duty  at  the 
mine  when  the  electrical  apparatus  or  machinery  is 
in  use  ;  and  at  such  time  as  the  amount  of  electricity 
delivered  down  the  mine  exceeds  200B.H.P.,a  com- 
petent person  shall  be  on  duty  at  the  mine  above 
ground,  and  another  below  ground.     Every  person 
appointed  to  work  any  electric  apparatus  shall  have 
been  instructed  in  his  duty  and  be  competent  for 
the  work  that  he  is  set  to  do. 

12.  No    person    shall    wilfully    damage,    interfere 
with,  or  without  proper  authority,  remove,  or  render 
useless,  any  electric  fine,  or  any  machine,  apparatus, 
or  part  thereof,  used  in  connexion  with  the  supply 
or  use  of  electricity. 

13.  Instructions  shall  be  posted  up  in  every  generat- 
ing,   transforming,    and    motor    house,    containing 
directions  as  to  the  restoration  of  persons  suffering 
from  electric  shock. 

14.  Direct  telephonic  or  other  equivalent  means 
of   communication   shall   be   provided   between   the 
surface  and  the  pit  bottom,    or  main  distributing 
centre  in  the  pit. 

15.  Within   three   months   after  the  introduction 
into  any  mine  of  electric  motive  power,  notice  in 
writing  must  be  sent  to  H.M.  Inspector  of  Mines  for 
the  district.     Notice  must  also  be  sent  of  any  existing 
electric  motive  power  installation  at  any  mine  within 
three  months  after  the  coming  into  force  of  these 
rules. 


168     ELECTRICAL  MINING  INSTALLATIONS 

16.  A  plan  shall  be  kept  at  the  mine  showing  the 
position  of  all  permanent  electrical  machinery  and 
cables  in  the  mine,  and  shall  be  corrected  as  often  as 
may  be  necessary  to  keep  it  up  to  a  date  not  more 
than  three  months  previously. 


SECTION  II 

GENERATING   STATIONS   AND   MACHINE   BOOMS 

17.  Where  the  generating  station  under  the  control 
of  the  owner  or  manager  of  the  mine  is  not  within 
400  yds.   of  the  working  pit  mouth,  an  efficiently 
enclosed  locked  switch  box  or  boxes,  or  a  switch 
house,  shall,  where  reasonably  practicable,  be  pro- 
vided near  the  pit  mouth,  for  cutting  off  the  supply 
of  electricity  to  the  mine. 

18.  There  shall  be  a  passage  way  in  front  of  the 
switch  board  of  not  less  than  3  ft.  in  width,  and  if 
there  are  any  connexions  at  the  back  of  the  switch- 
board, any  passage  way  behind  the  switchboard  shall 
not  be  less  than  3  ft.  clear.     This  space  shall  not  be 
utilized  as  a  storeroom  or  a  lumber  room,  or  ob- 
structed in  any  manner  by  resistance  frames,  meters, 
or   otherwise.     If   space   is   required   for   resistance 
frames  or  other  electrical  apparatus  behind  the  board, 
the  passage  way  must  be  widened  accordingly. 

No  cable  shall  cross  the  passage  way  at  the  back 
of  the  board  except  below  the  floor,  or  at  a  height  of 
not  less  than  7  ft.  above  the  floor. 

The  space  at  the  back  of  the  switchboards  shall  be 
properly  floored,  accessible  from  each  end,  and, 
except  in  the  case  of  low-pressure  switchboards,  must 
be  kept  locked  up,  but  the  lock  must  allow  of  the 
door  being  opened  from  the  inside  without  the  use 
of  a  key.  The  floor  at  the  back  shall  be  incombusti- 
ble, firm,  and  even. 

19.  Every    generator    shall    be    provided   with    a 


SPECIAL  RULES  169 

switch  on  each  pole  between  the  generator  and  the 
busbars. 

Where  continuous-current  generators  are  paral- 
leled, reverse  current  cut-outs  shall  also  be  provided. 

Suitable  instruments  shall  be  provided  for  measur- 
ing the  current  and  pressure  of  each  generator. 

Every  feeder  circuit  shall  at  its  origin  be  provided 
with  an  ammeter. 

20.  If  the  transmission  lines  from  the  generating 
station  to  the  pit  are  overhead,  there  shall  be  lightning 
arresters  in  connexion  with  the  feeder  circuits. 

21.  Automatic  cut-outs  must  be  arranged  so  that 
when  the  contact  lever  opens  outwards  no  danger 
exists  of  striking  the  head  of  the  attendant.     If  un- 
enclosed fuses  are  used  they  must  be  placed  within 
2  ft.  of  the  floor,  or  be  otherwise  suitably  protected. 

Where  the  supply  is  at  a  pressure  exceeding  the 
limits  of  medium  pressure,  there  shall  be  no  Jive  metal 
work  on  the  front  of  the  main  switchboard  within  8 
ft.  of  the  floor  or  platform,  and  the  space  provided 
under  Rule  No.  2  of  this  section  shall  be  not  less 
than  4  ft.  in  the  clear.  Insulating  floors  or  mats 
shall  be  provided  for  medium  pressure  boards  where 
live  metal  work  is  on  the  front  or  back. 

22.  All  terminals  and  live  metal  on  machines  over 
medium  pressure  above  ground,  and  over  low  pres- 
sure under  ground,  where  practicable  shall  be  pro- 
tected with  insulating  covers  or  with  metal  covers 
connected  to  earth. 

23.  No  person  other  than  an  authorized  person 
shall  enter  a  machine  or  motor  room,  or  interfere 
with  the  working  of  any  machine,  motor,  or  apparatus 
connected  therewith. 

SECTION  III 
CABLES 

24.  All    conductors    (except    as    hereinafter    pro- 
vided) shall  in  every  case  be  maintained  completely 


170  ELECTRICAL  MINING  INSTALLATIONS 

insulated  from  earth,  but  it  is  permissible  to  use  the 
concentric  system  with  earthed  outer  conductor,  if 
proper  arrangements  are  made  to  reduce  the  danger 
from  fire  or  shock  to  the  minimum ;  but  the  neutral 
point  of  polyphase  systems,  and  the  middle  wire  of 
three-wire  continuous-current  systems  may  be  earthed 
at  one  point. 

25.  Unless  fixed  as  far  as  is  reasonably  practicable 
out  of  reach  of  injury,  all  conductors,  other  than 
armoured  cables,   must  further  be  protected  by  a 
suitable  covering.     Where  lead-covered  cable  is  used 
the  lead  shall  be  earthed,  and  electrically  continuous 
throughout. 

The  exposed  ends  of  cables  where  they  enter  the 
terminals  of  switches,  fuses,  and  other  appliances, 
must  as  far  as  is  reasonably  practicable,  be  properly 
protected  and  finished  off,  so  that  moisture  cannot 
creep  along  the  insulating  material  within  the  water- 
proof sheath,  nor  can  the  insulating  material,  if  of 
an  oily  nature,  leak  out  of  the  cable. 

26.  All  joints  must  be  mechanically  and  electrically 
efficient,  and,  where  reasonably  practicable,  must  be 
suitably  soldered.     In  any  place  or  part  of  the  mine 
where  General  Rule  No.  8  of  the  Coal  Mines  Regula- 
tion Act,  1887,  applies,  suitable  joint  boxes  must  be 
used,   and  the  conductors  connected  by  means   of 
metal  screw  clamps,  connectors,  or  their  equivalent, 
constructed   in   a   safe   manner.     Provided   that   in 
any  place  or  part  of  a  mine  where  a  shot  may  be 
fired,  joints  may  be  soldered  by,  or  in  the  presence 
of,  a  person  authorized  in  that  behalf  by  the  manager  ; 
but  the  same  precautions  in  regard  to  examination 
and  removal  of  workmen  as  are  prescribed  by  para- 
graphs (/)  and  (i)  of  General  Rule  12  shall  be  ob- 
served in  all  cases,  and  where  the  place  is  dry  and 
dusty,  also  the  precautions  as  to  watering  prescribed 
in  paragraph  (h).     Wires,  other  than  signalling  wires, 
or  cables,  must  not  be  joined  by  merely  twisting 
them  together. 


SPECIAL  RULES  171 

27.  Overhead  bare  wires  on  the  surface  must  be 
efficiently  supported  upon  insulators,   and  clear  of 
any   traffic,    and   provided   with   efficient   lightning 
arresters. 

28.  All  cables  used  in  shafts  must  be  highly  in- 
sulated and  substantially  fixed.     Shaft  cables,  not 
capable  of  sustaining  their  own  weight,  shall  be  pro- 
perly supported  at  intervals   varying  according  to 
the  weight  of  the  cable.     Where  the  cables  are  not 
completely    boxed    in    and    protected    from    falling 
material,  space  shall  be  left  between  them  and  the 
side  of  the  shaft  that  they  may  yield,  and  so  lessen 
a  blow  given  by  falling  material. 

29.  Where  the  cables  in  main  haulage  roads  cannot 
be  kept  at  least  1  ft.  from  any  part  of  the  tub  or 
tram,    they    shall    be    specially    protected.     When 
separate  cables  are  used  they  shall,  if  reasonably 
practicable,  be  fixed  on  opposite  sides  of  the  road. 

The  fixing,  with  metallic  fastenings,  of  cables  and 
wires  not  provided  with  metallic  covering,  to  walls 
or  timbers,  is  prohibited. 

Cables  underground,  when  suspended,  shall  be 
suspended  by  leather,  or  other  flexible  material,  in 
such  a  manner  as  to  allow  of  their  readily  breaking 
away  when  struck,  before  the  cables  themselves  can 
be  seriously  damaged. 

Where  main  or  other  roads  are  being  repaired,  or 
blasting  is  being  carried  out,  suitable  temporary 
protection  must  be  so  used  that  the  cables  are  reason- 
ably protected  from  damage. 

30.  Trailing  cables  for  portable  machines  shall  be 
specially  flexible,  heavily  insulated,   and  protected 
with  either  galvanized  steel  wire  armouring,  extra 
stout  braiding,  hose  pipe,  or  other  effective  covering. 
Trailing  cables  shall  be  examined  at  least  once  in 
each  shift  by  the  person  in  charge  of  the  machine, 
and  any  defects  in  them  promptly  repaired. 

At  points  where  the  flexible  conductors  are  joined 
to  the  main  cables,  a  fixed  terminal  box  must  be 


172    ELECTRICAL  MINING  INSTALLATIONS 

provided,  and  a  switch  shall  be  fixed  close  to  or  in 
the  terminal  box  capable  of  entirely  cutting  off  the 
supply  from  the  terminal  box  and  motor. 


SECTION  IV 

SWITCHES,   FUSES   AND    CUT-OUTS 

31.  Fuses  and  automatic  cut-outs  shall  be  so  con- 
structed as  effectually  to  interrupt  the  current  when 
a  short  circuit  occurs,  or  when  the  current  through 
them  exceeds  the  working  current  by  200  per  cent. 
Fuses  shall  be  stamped  or  marked,  or  shall  have  a 
label   attached,   indicating   the   current  with  which 
they  are  intended  to  be  used,  or  where  fuse  wire  is 
used  each  coil  in  use  shall  be  so  stamped  or  labelled. 
Fuses  shall  only  be  adjusted  or  replaced  by  an  autho- 
rized person. 

32.  All  live  parts  of  switches,  fuses,  and  cut-outs, 
not  in  machine  rooms  or  in  compartments  specially 
arranged  for  the  purpose,  must  be  covered.     These 
covers  must  be  of  incombustible  material,  and  must 
be  either  non-conducting  or  of  rigid  metal,  as  far  as 
practicable,  clear  of  all  internal  mechanism. 

33.  All  points  at  which  a  circuit,  other  than  those 
for  signals,  has  to  be  made  or  broken,  shall  be  fitted 
with  proper  switches.     The  use  of  hooks  or  other 
makeshifts  is  prohibited,  and  in  any  place  or  part  of 
a  mine  where  General  Rule  No.  8  of  the  Coal  Mines 
Regulation  Act,  1887,  applies,  the  use  of  open-type 
switches,   fuses,   and   cut-outs  is   prohibited ;     they 
must  either  be  enclosed  in  gas-tight  boxes,  or  break 
under  oil. 

SECTION  V 
MOTORS 

34.  All  motors,   together  with   their  starting  re- 
sistances, shall  be  protected  by  switches  capable  of 


SPECIAL  RULES  173 

entirely  cutting  off  the  pressure,  and  fixed  in  a  con- 
venient position  near  the  motor ;  and  every  motor 
of  10  B.H.P.  or  over,  in  a  machine  room  underground, 
shall  be  provided  with  a  suitable  ammeter  to  indicate 
the  load  put  upon,  the  machine. 

35.  Where  unarmoured  cables  or  wires  pass  through 
metal  frames  or  into  boxes  or  motor  casings,  the 
holes  must  be  substantially  bushed  with  insulating 
bushes,  and,  where  necessary,  with  gas-tight  bushings 
which  cannot  readily  become  displaced. 

36.  Terminal  boxes  of  portable  motors  must  be 
securely  attached  to  the  machine,  or  be  designed  to 
form  a  part  thereof. 

37.  In  any  place  or  part  of  a  mine  where  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887-, 
applies,  all  motors,  unless  placed  in  such  rooms  as 
are  separately  ventilated  with  intake  air,  shall  have 
all  their  current-carrying  parts,  also  their  starters, 
terminals,   and  connexions,   completely  enclosed  in 
flame-tight  enclosures,  made  of  uninflammable  ma- 
terial, and  of  sufficient  strength  as  not  to  be  liable 
to  be  damaged  should  an  explosion  of  firedamp  occur 
in  the  interior,   and  such   enclosures   shall  not   be 
opened  except  by  an  authorized  person,  and  then 
only  when  the  current  is  switched  off.     The  pressure 
shall  not  be  switched  on  while  the  enclosures  are  open. 

38.  In  any  place  or  part  of  a  mine  where  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  a  safety  lamp  or  other  suitable  apparatus 
for  the  detection  of  firedamp  shall  be  provided  for 
use  with  each  machine  when  working,  and  should 
any  indication  of  firedamp  appear  on  the  flame  of 
the  safety  lamp   or  other  apparatus   used  for  the 
detection   of  firedamp,   the   person  in   charge   shall 
immediately  stop  the  machine,  cut  off  the  current  at 
the  gate  end  or  nearest  switch,  and  report  the  matter 
to  an  official  of  the  mine. 

39.  (a)  A    coal-cutter    motor   shall    not    be    kept 
continuously  at  work  for  a  period  of  time  exceeding 


174   ELECTRICAL  MINING  INSTALLATIONS 

a  maximum  period  which  shall  be  specified  in  writing 
by  the  manager,  so  that  the  roof  may  be  carefully 
examined. 

(b)  The  casing  or  inspection  doors  of  all  portable 
motors  used  underground  and  the  casings  of  their 
switches  and  other  appliances  shall  at  least  once  a 
week  be  opened  by  a  competent  person  appointed 
by  the  manager,  and  the  parts  so  disclosed  shall  be 
cleaned  and  examined  before  the  coverings  are  re- 
placed. In  special  cases  requiring  a  motor  to  run 
continuously,  longer  than  one  week,  the  motor  shall 
be  examined  at  the  end  of  the  run.  A  report  of  such 
examination  shall  be  entered  in  a  report  book. 

40.  The  person  in  charge  of  a  coal-cutter  or  drilling 
machine  shall  not  leave  the  machine  while  it  is  work- 
ing, and  shall,  before  leaving  the  working  place,  see 
that  the  current  is  cut  off  from  the  trailing  cables. 
He  must  not  allow  the  cables  to  be  dragged  along  by 
the  machine.     No  repairs  shall  be  made  to  any  port- 
able machine  until  the  pressure  has  been  cut  off  from 
the  trailing  cables. 

41.  If  any  electric  sparking  or  arc  be  produced 
outside  a  coal-cutting  or  other  portable  motor,  or  by 
the  cables  or  rails,  the  machine  shall  be  stopped,  and 
not  be  worked  again  until  the  defect  is  repaired,  and 
the  occurrence  shall  be  reported  to  an  official  of  the 
mine. 


SECTION  VI 

ELECTRIC  LOCOMOTIVES 

42.  Electric  haulage  by  locomotives  by  the  trolley 
wire  system  is  not  permissible  in  any  place  or  part 
of  a  mine  where  General  Rule  No.  8  of  the  Coal  Mines 
Regulation  Act,  1887,  applies.     On  this  system  no 
pressure  exceeding  the  limits  of  medium  pressure  may 
be  employed. 

43.  In  underground  roads  the  trolley  wires  must 


SPECIAL  RULES  175 

be  placed  so  that  they  are  at  least  7  ft.  above  the  level 
of  the  road  or  track,  or  elsewhere,  if  sufficiently 
guarded,  or  the  pressure  must  be  cut  off  from  the 
wires  during  such  hours  as  the  roads  are  used  for 
travelling  on  foot  in  places  where  trolley  wires  are 
fixed.  The  hours  during  which  travelling  on  foot  is 
permitted  shall  be  clearly  indicated  by  notices  and 
signals  placed  in  a  conspicuous  position  at  the  ends 
of  the  roads.  At  other  times  no  other  than  a  duly 
authorized  person  shall  be  permitted  to  travel  on 
foot  along  the  road. 

On  this  system  either  insulated  returns  or  unin- 
sulated metallic  returns  of  low  resistance  may  be 
employed. 

44.  In  order  to  prevent  any  other  part  of  the 
system  being  earthed  (except  when  the  concentric 
system  with  earthed  outer  conductor  is  used)  the 
current  supplied  for  use  on  the  trolley  wires  with  an 
uninsulated  return  shall  be  generated  by  a  separate 
machine,  and  shall  not  be  taken  from  or  be  in  con- 
nexion   with    electric    lines    otherwise    completely 
insulated  from  earth. 

45.  If  storage  battery  locomotives  are  used  in  any 
place  or  part  of  a  mine  where  General  Rule  No.  8  of 
the  Coal  Mines  Regulation  Act,   1887,  applies,  the 
rules  applying  to  motors  in  such  places  shall  also  be 
deemed  to  apply  to  the  boxes  containing  the  cells. 


SECTION  VII 

ELECTRIC  LIGHTING 

46.  All  arc  lamps  shall  be  so  guarded  as  to  pre- 
vent pieces  of  ignited  carbon  falling  from  them,  and 
shall  not  be  used  in  situations  where  there  is  likely 
to  be  danger  from  the  presence  of  coal  dust.     They 
should  be  so  screened  as  to  prevent  risk  of  contact 
with  persons. 

47.  Small  wires  for  lighting  circuits  must  be  either 


176   ELECTRICAL  MINING  INSTALLATIONS 

conveyed  in  pipes  or  casings,  or  suspended  from  por- 
celain insulators,  or  tied  to  them  with  some  non- 
conducting material  which  will  not  cut  the  covering, 
and  so  that  they  do  not  touch  any  timbering  or  metal 
work.  On  no  account  must  staples  be  used.  If 
metallic  pipes  are  used  they  must  be  electrically 
continuous  earthed.  If  separate  uncased  wires  are 
used  they  must  be  kept  at  least  2  in.  apart,  and  not 
brought  together  except  at  lamps  or  switches  or 
fittings. 

48.  In  any  place  or  part  of  a  mine  where  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  electrical  lamps  if  used  must  be  of  the  vacuum 
or  enclosed  type  ;    they  shall  be   protected  by  gas- 
tight  fittings  of  strong  glass,  and  have  no  flexible 
cord  connexions,  and  shall  only  be  changed  by  a 
duly  authorized  competent  person.     While  the  lamps 
are  being  changed  the  current  shall  be  switched  off. 

49.  In  all  machine  rooms  and  other  places  under- 
ground, where  a  failure  of  electric  light  is  likely  to 
cause  danger,   some  safety  lamps   or  other  proper 
lights  shall  be  kept  for  use  in  the  event  of  such  failure. 


SECTION  VIII 

SHOT-FIRING 

50.  Electricity  from  lighting  or  power  cables  shall 
not  be  used  for  firing  shots,  except  in  sinking  shafts 
or  stone  drifts,  and  then  only  when  a  special  firing 
plug,  button,  or  switch  is  provided,  which  plug, 
button,  or  switch  shall  be  placed  in  a  fixed  locked 
box,  and  shall  only  be  accessible  to  the  authorized 
shot-firer. 

The  firing  cables  or  wires  shall  not  be  connected 
to  this  box  until  immediately  before  it  is  required 
for  the  firing  of  shots,  and  shall  be  disconnected 
immediately  after  the  shots  are  fired. 

When  shot-firing  cables  or  wires  are  used  in  the 


SPECIAL  RULES  177 

vicinity  of  power  or  lighting  cables,  sufficient  pre- 
cautions shall  be  taken  to  prevent  the  shot-firing 
cables  or  wires  from  coming  in  contact  with  the 
lighting  or  power  cables. 

The  foregoing  rules  shall  not  apply  to  telephone, 
telegraph,  and  signal  wires,  to  which  the  rules  of  this 
section  only  shall  apply. 


SECTION  IX 

SIGNALLING 

51.  All  proper  precautions  must  be  taken  to  pre- 
vent electric  signal  and  telephone  wires  from  coming 
into  contact  with  other  electric  conductors,  whether 
insulated  or  not. 

52.  Contact  makers  or  push  buttons  of  electric 
signalling  circuits  shall  be  so  constructed  and  placed 
as  to  prevent  the  circuit  being  accidentally  closed. 

53.  In  any  place  or  part  of  a  mine  where  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  bare  wires  shall  not  be  used  for  signalling 
circuits  except  in  haulage  roads,  and  the  pressure 
shall  not  exceed  15  volts  in  any  one  circuit. 

SECTION  X 

ELECTRIC  RELIGHTING  OF  SAFETY  LAMPS 

54.  In  mines  to  any  place  or  part  of  which  General 
Rule  No.  8  of  the  Coal  Mines  Regulation  Act,  1887, 
applies,  when  safety  lamps  are  relighted  underground 
by  electricity,  the  manager  shall  select  a  suitable 
station  or  stations,  which  are  not  in  the  return  air- 
way, and  in  which  there  is  not  likely  to  be  any  accu- 
mulation of  inflammable  gas  ;    and  no  electric  re- 
lighting apparatus  shall  be  used  in  any  other  place. 
All  electrical  relighting  apparatus  shall  be  securely 
locked,  so  as  not  to  be  available  for  use  except  by 
persons  authorized  by  the  manager  to  relight  safety 


178  ELECTRICAL  MINING  INSTALLATIONS 

lamps,   and  such   persons  shall  examine  all  safety 
lamps  brought  for  relighting  before  they  are  re-issued. 

SECTION  XI 

EXEMPTIONS   AND   MISCELLANEOUS 

55.  Notwithstanding  anything  contained  in  these 
rules,  any  electrical  plant  or  apparatus  installed  or 
in  use  before  the  coming  into  force  of  these  rules  may 
be  continued  in  use  unless  an  inspector  shall  other- 
wise direct,  or  subject  to  any  conditions  affecting 
safety  that  he  may  prescribe. 

In  case  any  difference  of  opinion  shall  arise  between 
an  inspector  and  an  owner  under  this  Rule,  the  same 
shall  be  settled  as  provided  in  Section  42  of  the  Coal 
Mines  Regulation  Act,  1887. 

56.  Any  of  the  foregoing  requirements  shall  not 
apply  in  any  case  in  which  exemption  is  obtained 
from  the  Secretary  of  State,  on  the  ground  either  of 
emergency  or  special  circumstances,  on  such  conditions 
as  the  Secretary  of  State  may  prescribe. 


INDEX 


Adhesion     of     Locomotives, 

106 
Alternators,  16 

—  output  of,  20 

—  parallel  running,  29 

—  power  to  drive,  24 
Aluminium  conductors,  44 
Ampere  meters,  26 
Apparent  watts,  9 
Armouring  of  cables,  68 


Battery  load  equalizers,  152 
Boiler-house  plant,  13 
Boving  turbine  pump,  109 
Brakes,  emergency,  161 

—  rheostatic,  105 

—  regenerative,  150 

—  for  winding  engine,    145 

C 

Cables,  aluminium,  44 
Cable  boxes,  72-75 

—  cleats,  66 

—  drums,  122 

—  shaft,  62 

—  suspenders,  66,  71 

—  trailing,  76 

—  underground,  62 
Capacity  of  wires  and  cables, 

52-61 

Choking  coils,  49 
Circuit  breakers,  26 
Coal-cutting,  123 
Coal-cutters,  types  of,  124 
Coal-cutter  motors,  124 


Conductors,  aerial,  44 

—  bare,  42 

—  determination  of  size,  42 

—  and  insulation,  63 

—  method  of  laying,  69 
Controllers  for  haulages,  92 

—  liquid,  92,  161 

—  oil  immersed,  91 
Current  density,  40 

D 

Depth  indicators,  141 
Dip  pumps,  122 
Drilling,  126 

Drums  for  winding  engines, 
142 

E 

Earthing,  19 
Earth  plates,  47 

—  wires,  84 

Electric  generators,  continu- 
ous current,  15 
alternating  current,  18 

—  lighting,  85 
Engines,  13 
Equalizing  switches,  27 

F 

Fans,  electrically  driven,  129 

—  power  required  to  drive, 
130 

—  regulation  of,  131 
Flexible  couplings,  119 

—  cable  suspenders,  71 
Fly-wheel  converter,  148 

—  equalizer,  146 


180 


INDEX 


Frequency,  19 
Friction  in  pipes,  118 
Fuses,  32 

G 

Gas  engines,  12 
Gate  end  boxes,  77 
Generating  plant,   11 
Generators,  electric,  con- 
tinuous current,   15 

—  with   inter-poles,    16 

—  alternating  current,  18 

—  —  speed  of,  19 

—  power  required  to  drive, 

21 


H 

Haulage,  electric,  87 
• —  main,  96 

—  main  and  tail,  97,  98 

—  endless  rope,  99 

—  controllers,  92 

—  motors,  91 
rating,  90 

—  resistances,  92 

Home  Office  Regulations,  163 

—  cables,  169 

—  definitions,  163 

—  exemptions,  178 

—  general,  164 

—  generating  stations,  168 

—  lighting,  176 

—  locomotives,  174 
— -  miscellaneous,  178 

—  motors,  172 

—  safety  lamps,  177 

—  shot  firing,  176 

—  signalling,  177 

—  switches,  fuses,  etc.,  172 
Horse-Power  for  coal  cutters, 

126 
• —  for  generators,  21 

—  for  haulages,  96-102 

—  for  pumps,  117 

—  for  ventilating  fans,  113 

—  for  winding,  135-140 


Impedance,  8 
Induction  motors,  112 
Instrument  transformers,  30 
Interpoles,  16 
Isolating  switches,  32 

K 

Kelvin's  law,  41 

Keope  pulley,  143 

Kilo  volt  amperes  (K.V.A.), 

22 
Kinetic  energy,  146 


Lagging  currents,  7 
Leakage  indicators,  35 
Lightning  arresters,  47 
Lighting,  electric,  85 

—  transforms,  85 
Lock-coil  armouring,  68 
Locomotives,  electric,  102 

—  equipment,  105 

M 

Motors,  alternating  current, 
14 
-  speed  of,  116 

—  —  starting  performance, 
113 

Motor  generators,   14 
Motors  for  haulage,  90-91 

—  for  fans,  131 

N 

Nalder    Bros.'  leakage    indi- 
cator, 35 

O 

Ohm's  law,  3-8 
Oil-immersed  controllers,  91 
Oil  switches,  28 


Parallel  drums,  142 


INDEX 


181 


Pipe  friction,  118 
Poles,  45 

Power  factor,  9,  10 
Pressure  drop,  3,  8,  21 
Pumps,  Cornish,  107 

—  dip,  122 

—  motors  for,  111,  113 

—  plunger,  108 

—  power  required,  117 

—  priming,   130 

—  speed  of,  110 

—  sinking,  119, 

—  turbine,  109 

R 

Bam  pumps,  108 
Reel  drums,   144 
Regenerative  braking,  180 
Regulation  of  motors,   131- 

133 

Relays,  33 
Resistance,  3 

—  of  conductors,  51-61 
Reversible  booster,  154 
Rheostats,  26,  30 
Rope  speeds,  145 

8 

Short  circuiting  devices,  115 
Short  circuited  rotors,  113 
Siemen's  Ilgner  system,  147 
Sinking  pumps,  119 

control,  126 

Slip  of  induction  motors,  116 
Speed  of  induction  motors, 
116 

—  control,  131 
Spiro-conical  drums,  143 
Starting  resistances,   113 

—  transformers,   113 
Star-mesh  starters,  114 
Stranded  cables,  52-61 
Switches,  equalizing.  27 

—  isolating,  32 

—  oil,  28 


Switch-gear    for    continuous 
current,  25 

—  for  alternating  current,  28 

—  for    haulage    motors,    92 
Suspension  of  conductors,  44 
Synchronizers,  29 


Terminal  poles,  48 
Time  limit  relays,  3?^ 
Trailing  cables,  126 
Transf ormers  ]f or  lighting,  85 

—  for  instruments,  28-30 
Transmission,  39 

—  poles,  48 
Trip  coils,  29 

Trolley  for  locomotive,   105 
Turbines,  13 
Turbine  pump,  109 


Valves,  non-return,  120 
Ventilating,  electric,  129 

—  fans,  130 
Voltage  drop,  21 

—  continuous,  3 

—  alternating,  6 
Volt  meter,  26 

—  paralleling,  27 

W 

Watts,  apparent,  9 

—  true,  3,  9 
Watt  meters,  34 

Weight  of  conductors,  52*61 
Winding,  electric,  134 

acceleration,  139 

efficiency,  140 

—  load  curve,  138,  151 

—  speed  of,  137 

—  system,  Crompton's,   152 

—  —  Siemen's    Ilgner,    147 
Westinghouse,  157 


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